THE GETTY CENTER LIBRARY Digitized by the Internet Archive in 2016 https://archive.org/details/chemistryforphotOOtown CHEMISTRY FOR PHOTOGRAPHERS. BY CHAS. F. TOWNSEND, F.C.S., F.R.P.S. ILL USTRA LED. I B NEW YORK ; SPON & CHAMBERLAIN. 12 CORTLANDT ST CONTENTS. CHAP. PAGF. I. Introduction . . ‘5 II. Chemistry Generally, and the Chemistry of THE Silver Salts in particular, ... 13 III. The Chemistry of the Photographic Image, . 36 IV. Developers, 53 V. Reversal, 79 VI. Reduction, Intensification, &c., ... 83 VII. Printing in Silver 88 VIII. Printing in Salts of Iron, . ... 102 IX. Printing in Platinum, ..... 105 X. The Bichromate Printing Processes, . . 109 XI. Orthochromatism, ...... 115 XII. Impurities and Substances that Alter in the Air, ........ 118 XIII. Recovery of Residues, ..... 123 XIV. Cellulose, . . , 125 XV. Resins, Varnishes, &c., 129 Cyclopedic Index, 140 CHEMISTRY FOR PHOTOGRAPHERS. CHAPTEE I. Introductory. - The first essentials to anyone studying chemistry are accuracy and cleanliness. Most of the surpris- ing results obtained by students in their early days are due to want of cleanliness. Another point I should like to impress upon those just taking up the subject is that learning “ facts ” in a more or less mechanical way is not learning chemistry. It is said that a good lawyer does not know much law, but knows where to find his law. The same applies to a good chemist. Above all, endeavour to get an insight into the nature of things, and remember that the proper place for a dictionary is not inside a man’s head, but on a shelf. If particular sets of facts or figures are often required for reference, don’t try to learn them, but cut or copy them out, give them a coat of varnish and paste them on the 6 PRELIMINARY HINTS. work-room door. There is still another point : never take for granted any statement you read if you pos- sess the means of testing it and have five minutes to spare. Even if the statement is correct, more knowledge will be gained by merely seeing the thing V V Fig. 1. happen than by reading about it all day. Statements in photographic and other scientific books are fre- quently incorrect, having crept into an early text- book by mistake and been copied religiously ever since. Mistakes have a way of creeping into a book, MEASUKING APPARATUS. 7 however carefully it is written, so test all statements when an opportunity occurs. As all chemical and photographic work is based on measurement, it is important to have a rational system of weights and measures. For this reason it would be well if every photographer discarded the XI - i\ Fig. 2. system of the pharmacist, together with his measur- ing apparatus, replacing ounces and minims by grams and cubic centimetres, and conical graduates by burettes and pipettes. The conical measures now in use are bad in every way : it is practically impossible to measure accurately with them, and they are very difficult to keep clean. 8 BURETTES AND PIPETTES. The construction of a burette will readily be seen from the figure (fig. 1). The instrument can be purchased with a glass tap, or with a glass jet, a piece of india-rubber tubing and a pinchcock, the latter being quite as convenient and much cheaper. For photographic purposes, burettes for the different developing solutions should be suspended round the sink as shown in the sketch (fig. 2), being fed from stock bottles on a shelf above, when large quantities of material are used. It is well to have an opal glass plate at the back of the fixed burette, and to read the level of the bottom of the black curve at the top of the liquid when measuring. A float with a line engraved on it is sometimes used for reading, and has the advantage of keeping the solution from the air as well as or better than a stopper. The construction of a pipette will be seen from the last part of figure 1. It is filled by drawing up the liquid with the mouth : the finger is then placed rapidly on the top, and the liquid is allowed to run down to the mark. The pipette with its contents is then transferred bodily to the vessel, into which it is required to run the liquid. In the metric system, the centimetre is the measure of length, the cubic centimetre the measure of capacity, and the weight of 1 cubic centimetre of water at 15° C., or the gram, is the measure of weight. How delightfully simple these are, com- pared to the complicated and heterogeneous measures of the pharmacist ! An inch is about centi- WEIGHTS AND MEASURES. 9 metres, and an ounce about 28 grams, a fluid ounce being 28 cubic centimetres. For larger measures the litre containing 1000 c.c., and the kilogramme or kilo, of 1000 grams, are used. For small measures the decimals of the gram and the centimetre are employed. Going up the scale, 10, 100, 1000, etc., grams and centimetres follow in order, and going down the scale -jL, yoVo ^ gram or centi- metre follow one another, the decimal system being employed throughout. It is convenient to remember that a litre is very nearly a pint and three-quarters. The following table gives the means of converting English into metric equivalents, and vice versd. TABLE I. — Weights and Measures in British and Metric Systems. APOTHECARIES’ WEIGHT (by which Formul.® are made up). 20 grains =:! scrapie . . = 1*296 grams. 8 drachms = 1 ounce = 480 grains == 31 '1 ,, 3 scruples = 1 drachm = 60 ,, = 3*887 ,, 12 ounces = l pound = 5760 ,, =373*2 ,, AVOIRDUPOIS WEIGHT (by which Chemicals are sold). 437| grains = 1 ounce . . . = 28*4 grams. 1 6 ounces = 1 pound = 7 000 grains = 453 *59 , , METRIC SYSTEM— WEIGHT. 10 milligrams = 1 centigram . . . = *1543 grain. 10 centigrams = 1 decigram = 100 milligrams = 1*543 ,, 10 decigrams =1 gram = 100 centigrams = 15'432 ,, 10 grams =1 decagram . . . =154*323 ,, 10 decagrams =1 hectogram = 100 grams . =3 ozs. 227| grains. 10 hectograms = 1 kilogram =1000 grams . =35 ozs. 87^ 10 TEN PER CENT. SOLUTIONS. MEASURES OF LENGTH. British. 3 barley-corns = 1 inch . . = 2*54 cm. 12 inches . =1 foot . . =30*48 ,, 3 feet . = 1 yard = 36 inches = 91*44 , , Metric. 10 millimetres = 1 centimetre = *3937 inch or H approx. 10 centimetres = 1 decimetre = 3’937 ,, 10 decimetres =1 metre =39*37 ,, FLUID MEASURE. 1 drachm . . . = 3 *5 cubic centimetres. 1 ounce = 480 minims = 28*4 ,, ,, 1 pound =5760 „ =340*8 ,, ,, 1 pint* . . . =568*0 ,, ,, 1 quart = 40 ounces = 1*136 litres. 1 gallon = 160 ,, = 4*544 „ METRIC SYSTEM— FLUID. 1 cubic centimetre (c.c.) . . . = 17 minims. 10 ,, ,, =1 centilitre . . =170 ,, 10 ,, centilitres =1 decilitre = 100 c.c. = 3*52 fl. oz. 10 ,, decilitres =1 litre =1000 c.c. = 35*2 ,, * The American pint is 16 ounces. Many photographers have realised the con- venience of a rational system, and in addition to discarding the aboriginal system of weights and measures have adopted ten per cent, solutions for all their work. From these any developer or other dilute solution can be made up in a minimum of time. In cases of stock solutions and one or two other instances it is convenient to have a fifty per cent, solution, and in other cases five per cent., or perhaps one per cent., solutions must be employed, owing to the difficulty of dissolving a par- ' 60 minims = 8 drachms = 12 ounces = 20 ounces = 2 pints = 4 quarts = SCALES OF TEMPERATURE. 11 ticular substance, but solutions should always be made up to contain so many parts per cent. Some confusion in the reader’s mind may be saved by pointing out again that a cubic centimetre of water weighs one gram and a ten per cent, solu- tion is understood to mean ten grams of the sub- stance in one hundred of water, or one hundred grams in a litre, i.e., ten grams dissolved in part of the water, and the whole made up to an even hundred, not to a hundred and ten. Temperature is measured in this country by Fahrenheit’s scale, on which the freezing point of water is 32°, and the boiling point 212°, zero being 32° below freezing point. In the Centigrade or Celsius scale employed in scientific work, and in general practice in some parts of the continent, the freezing point of water is zero and the boiling point 100°. Table II. enables you to convert one scale into the other. The only mathematical signs used in the explana- tions will be + added to - subtracted from X multiplied by -r divided by = equals and the signs for a proportion, namely. As is to so is to the figure required, 2 : 4 : : 3 : that is to say. 4x3~2 = G. 12 COMPAKISON OF THERMOMETERS. TABLE 1 1. — Thermometers. Comparison op Fahrenheit and Centigrade (Celsius) Scales. Cent. Fahr. Cent. Fahr. Cent. Fahr. 100 B. 212 B. 65 149 30 86 99 210*2 64 147*2 29 84*2 98 208*4 63 145*4 28 82*4 97 206*6 62 143*6 27 80*6 96 204*8 61 141-8 26 78*8 95 203 60 140 25 77 94 201*2 59 138-2 24 75*2 93 199*4 58 136*4 23 73*4 92 197*6 57 134*6 22 71*6 91 195*8 56 132*8 21 69*8 90 194 55 131 20 68 89 192*2 54 129*2 19 66*2 88 190*4 53 127*4 18 64*4 87 188-6 52 125*6 17 62*6 86 186*8 51 123*8 16 60*8 85 185 50 122 15 59 84 183*2 49 120*2 14 57*2 83 181*4 48 118*4 13 55*4 82 179-6 47 116*6 12 ’ 53*6 81 177*8 46 114*8 11 51*8 80 176 45 113 10 50 79 174*2 44 111*2 9 48*2 78 172*4 43 109*4 8 46*4 77 170*6 42 107*6 7 44*6 76 168*8 41 105*8 6 42*8 75 167 40 104 5 41 74 165*2 39 102*2 4 39*2 73 163*4 38 100*4 3 37*4 72 161*6 37 98*6 2 35*6 71 159*8 36 96*8 1 33*8 70 158 35 95 Zero 32 69 156*2 34 93-2 68 154*4 33 91*4 67 152*6 32 89*6 66 150*8 31 87*8 DIRT. 13 CHAPTEK IL Chemistry generally, and the Chemistry of the Silver Salts in particular. At the beginning of the book mention was made of the importance of cleanliness. “ Dirt ” in a chemical sense is much more comprehensive than is usually understood. To get any vessel chemically clean is not an easy process, and a vessel after containing most chemicals requires several careful washings before it is fit for use again. The diffi- culty about chemical dirt is that it is not always visible to the eye. The porcelain dish used to con- tain the “ hypo ” bath may look beautifully clean after it has been washed out, yet the porcelain is probably saturated with “ hypo ” which will dissolve into the next solution placed in the dish, if used for anything but “hypo,” and spoil all the plates and paper it comes into contact with. Three care- ful washings are generally sufficient to cleanse an article thoroughly, but in cases where very careful cleansing is required, such as plates used for coating in the wet plate process, a powerful mixture, such as the following, must be employed, which burns up 14 WASHING. any dirt. Never allow the mixture to get on to clothes or fingers ! Potassium bichromate, . . 50 grams, . 1 oz. Sulphuric acid (commercial), . 50 c.c., . 1 „ Water, .... 1000 c.c., . 20 ozs. Dissolve the bichromate in the water, and when dissolved add the sulphuric acid in a thin stream, stirring the while. Por some purposes it is con- venient to use much more sulphuric acid. Einse well under the tap when clean. The solu- tion, if no water is added to it, may be used over and over again until exhausted. Perhaps it will be well to define what is meant by “ washing.” In regard to utensils it is used in the ordinary sense, but when employed in connection with prints and negatives a wrong impression is often conveyed. When a photographer says “ wash,” he generally means “ soak.” In a recently fixed negative, for example, the “ hypo ” must be removed from the film by soaking it out. A constant diffusion goes on between the solution of “ hypo ” in the film and the clean water in contact with it. At first this diffusion proceeds very rapidly, and then more and more slowly as the “ hypo ” in the film becomes dilute. No advantage is to be gained, therefore, by allowing the water to run furiously over the surface of the plate, as force does not assist the operation, and the water must be left in contact with the film for a sufficient time to take up ATOMS. 15 its allowance of “ bypo.” Eunning water is a distinct advantage, although frequent changes and rocking of the dish do nearly as well, but the water may run as slowly as you please, and should how into the upper part of the whole contents of the vessel, but out from the lower part. A syphon should be used to remove the water from all deep washing tanks. Mention will be made directly of atoms and molecules, so that I had better explain what is meant by these terms, and by a chemical element. If pure iron is ground up very small and acted upon by the strongest forces that the chemist can bring to bear upon it, nothing but iron can be obtained from it. The substance cannot be split up into two other materials, so that chemists call it and all such substances “ elements.” If the powdered iron that was spoken of just now be examined under the microscope, it will be seen that the particles would bear splitting up very much smaller. Chemists have come to the conclusion, that if human eyesight and fingers were keen enough to go on splitting up these microscopic particles, a stage would be reached when the particles could be made no smaller. These ultimate particles are called “ atoms.” All the atoms of iron, for instance, may be considered as being exactly alike and of the same size and weight. As it is not possible to examine the actual atoms, equal quantities of the different elements are compared with one another. 16 CHEMICAL ELEMENTS. In this way it is found that the iron atom is 56 times as heavy as the hydrogen atom, which, being the lightest, is called 1 and is used as the standard of atomic weight. The silver atom is 108 times as heavy as the hydrogen atom, so that the atomic weight of silver is 108, and that of iron 56. These atoms combine with one another to form “ molecules,” so that a molecule is compounded of atoms. The iron atom, for instance, may combine with another iron atom to form an iron molecule, or it may com- bine with one or more atoms of some other element, such as chlorine (see later), to form a molecule of iron chloride. Now I want you to realise that nothing ever happens by chance in chemistry. Similar quantities of the same substances, acting in the same way, always produce the same result, and the same quantity of it, as you will see directly. For convenience, chemists employ a kind of shorthand, using symbols for the different sub- stances. H stands for hydrogen and for 1 gram or ounce, or whatever it may be, of hydrogen ; Fe (Latin, ferrum) stands for iron and for 56 grams, or whatever it may be, of iron, and so on. The following symbols for different elements will be used in this chapter ; particulars of the others will be found in the index : — Atomic Hydrogen, Oxygen, Nitrogen, Name. Symbol. Weight. . H 1 . O 16 . N 14 WATER. 17 Sulphur, . S 32 Carbon, .... . c 12 Chlorine, . Cl 35*5 Bromine, . Br 80 Iodine, .... . I 126-5 Sodium, . Na 23 Potassium, . K 39 Silver, .... . Ag 108 Coal gas is a mixture of various inflammable gaseous materials, but amongst them contains a large proportion of a gas called hydrogen. When this burns, it combines with the oxygen in the air — another gas — -to form water. If a cold plate or piece of metal be held for a second or two over a gas flame and then withdrawn, the surface will be coated with moisture (the soot need not enter into the question). It has been found, from a large number of experiments, that a particle of water consists of two atoms of hydrogen, each weighing 1, combined with one atom of oxygen weighing 16, and is represented chemically as HOH (or HgO), the total weight (1 + 16 + 1) being 18. Sodium is a metal, quite soft at ordinary tempera- tures, but its freshly cut surface is bright and metallic looking. If a piece about the size of a large pin’s head be dropped into water, a great commotion ensues and bubbles of gas are given off, which take Are if a light is applied to them, and sometimes do so on their own account. This gas is hydrogen. The atoms of sodium (Na) are turning B 18 CAUSTIC SODA. out half the hydrogen atoms from the water, thus : — Water. Sodium. Caustic Soda. Hydrogen. HOH + Na = NaOH + H escaping, added to forms and Instead of water there is now a weak solution of caustic soda, which turns red litmus -paper blue, changes acids into substances that are not acid but neutral, and is called an alkali. If more sodium be added to the solution, more hydrogen will be turned out, the alkaline solution becoming stronger, forming in the end a solid mass of caustic soda, which could be run into moulds to make the familiar white sticks. It has been shown that a particle or molecule, as chemists term it, of water (HOH) weighs 18. In caustic soda (HaOH) there is an atom of sodium (Na) occupying the place of one of the H’s, weighing 1. How an atom of sodium is twenty- three times as heavy as an atom of hydrogen, so that caustic soda (NaOH) weighs 40 (23 + 16-f 1). This means that if 23 grams, ounces, or lbs. of sodium were cut up into small pieces and dropped into 18 grams, ounces, or lbs. of water, 40 grams, ounces, or lbs. of caustic soda would be obtained, than which nothing could be simpler. All chemical formulae can be expressed in actual weights in just the same manner. The formulae that appear so alarming are merely this convenient and scientific kind of shorthand, the key to which will be found on page 138. HYDROCHLORIC ACID. 19 Chlorine is a yellowish-green, very irritating gas. If the reader wishes to become acquainted with it let him warm ten drops of hydrochloric acid with five drops of nitric acid in a test-tube or other glass vessel, when fumes of chlorine will be freely given off. This yellowish-green gas combines violently with hydrogen to form hydrochloric acid (HCl), one atom of the one combining with one atom of the other. What is ordinarily called hydrochloric acid and purchased of a chemical dealer is a solution of hydrochloric acid gas ; this solution will be found to turn blue litmus red, to be intensely acid to the taste (dilute), and to be exactly the opposite of the alkaline caustic soda. If caustic soda be mixed with hydrochloric acid in proper proportions a neutral liquid will be obtained. A good deal of heat is given out, and the experiment must be tried with dilute acid and alkali. The resulting liquid is called “ neutral,” because it is neither acid nor alkaline, and has no effect on litmus-paper ; it is, in fact, a solution of a salt — common salt or sodium chloride. What has just happened is represented in chemi- cal shorthand thus: — Hydrochloric Sodium Acid. Caustic Soda. Chloride. Water. HCl + NaOH = NaCl -f- HOH. added to forms and This is called an “ equation,” because there is an equal quantity of material on both sides, but it is 20 EQUATIONS. arranged differently. Whenever anything happens in chemistry there is the same quantity of material at the end as there was at the beginning. Nothing is ever destroyed; the different parts are merely rearranged. Now take a solution of silver nitrate. If you have the means of weighing and measuring accur- ately, make up a 1 per cent, solution of silver nitrate by dissolving 1 gram in 100 c.c. of distilled water; fill a burette with the solution and run exactly 34 c.c. into a dish or gallipot of some kind. Make up a 1 per cent, solution of sodium chloride (1 gram in 100 c.c.); put this in another burette, and out of this run 10 c.c. into the gallipot con- taining the 34 c.c. of silver nitrate. A white “ precipitate ” will form ; shake the vessel round and allow the precipitate a few moments to settle to the bottom. Then add a few more drops from the sodium chloride burette. A fresh white pre- cipitate will form and sink to the bottom. This precipitate will go on forming until 11*7 c.c. alto- gether of sodium chloride solution have been added. If the solution be now allowed to stand until the precipitate has settled, no more precipitate will form when more sodium chloride is run in. If the reader has not conveniences for measuring, he must take a small quantity of silver nitrate solution and add solution of common salt in small quantities at a time until no more precipitate is thrown down. To explain what has been happening, it is necessary SILVEK CHLORIDE. 21 to say a few words about silver nitrate. Nitric acid contains one atom each of hydrogen and nitrogen and three atoms of oxygen. As hydrochloric acid is HCl, so nitric acid is HNO 3 . When silver (Ag) is dissolved in nitric acid, the silver takes the place of the hydrogen, producing silver nitrate (AgN 03 ). When the sodium chloride was run into the silver nitrate in the experiment, the sodium and the silver changed places. Silver Mtrate. Sodium Chloride. Silver Chloride. Sodium Nitrate. AgNOg + NaCl = AgCl + NaNOg. The white precipitate was silver chloride, and the sodium nitrate remained dissolved in the solution. Further, it was seen from the experiment that 11’7 parts of sodium chloride were just sufficient to cause all the silver in 34*0 parts of silver nitrate to pre- cipitate as chloride. If the different parts of the equation are calculated out, it will be seen that this is the case. Ag N O 3 + Na Cl = Ag Cl + Na N O 3 108 + 14 + 48 23 + 35-5 108 + 35-5 23 + 14 + 48 170 58-5 14^5 S So that 170 AgNOg requires 58‘5 NaCl, or 340 requires 117. From this equation it will be seen also that from 170 parts of silver nitrate 143’5 parts of silver chloride can be obtained. This calculation, or similar calculations with bromide and iodide instead of chloride, are being gone through 22 CHLORIDE, BROMIDE, AND IODIDE. constantly when making emulsions. Although tables are given to save time, every photographer should know how to work out the figures himself if necessary. Potassium (K) is a very similar metal to sodium, and it is sometimes more convenient to use potassium salts, such as potassium bromide and potassium iodide, instead of sodium salts, but the calculations are exactly similar, using K (39) in place of Na (23). Bromine is a red liquid and iodine a brownish, rather metallic looking, solid. They resemble chlorine very closely, and silver bromide and iodide are very like silver chloride. Take two gallipots and place silver nitrate solution in each. Into one run a solution of potassium bromide, and into the other a solution of potassium iodide. A precipitate will be formed in each case ; that with the bromide being yellowish- white (silver bromide), and that with the iodide being pale yellow (silver iodide). These experiments can all be performed in test-tubes, i.e., thin glass tubes closed at one end, or in beaker flasks ; the latter (fig. 3) are useful for many purposes in the work-room. As silver chloride, bromide, and iodide resemble one another so closely in their chemical properties, they can often be substituted for one another partly or wholly without introducing any very great change in the result. In making emulsions for dry plates or in preparing collodion for wet plates, these salts are introduced in varying proportions to suit the EQUIVALENT QUANTITIES. 23 subject. Accordingly it is important to know what quantity of chloride is equivalent to a certain quantity of bromide or iodide, and vice versa. This can be learned from chemical shorthand at once. The formulae for the three compounds are AgCl, AgBr, and Agl. An atom of bromine (Br) weighs 80 and iodine (I) weighs 126*5 ; so that Silver chloride, AgCl, weighs 108+ 35*5 or 143*5 „ bromide, AgBr, „ 108+ 80 „ 188 „ iodide, Agl, „ 108 + 126*5 ,, 234*5 From this it is clear that 143*5 parts of the chloride are capable of doing the same work as 188 parts of bromide or 235 of iodide. The following table gives equivalent quantities of these salts to save calculations. TABLE III. — Equivalent Quantities of Silver Salts. Silver (Metallic). Nitrate. Chloride. Bromide. Iodide. 1 1*574 1*328 1-741 2-176 0-6353 1 0-844 1-106 1-38-2 0*7523 1*184 1 1-310 1-638 0-5744 0-904 0-763 1 1-250 0*4595 0-723 0-610 0-800 1 Take the three vessels containing the precipitates — silver chloride, bromide, and iodide — and decant off the liquid with the help of a glass rod as shown in the sketch (fig. 4). To the first add a few drops 24 EXPERIMENTS. of ammonia solution ; the silver chloride will dis- solve completely. To this solution add a few drops of acid to neutralise the ammonia ; the white silver bromide will reappear, showing that, although it is soluble in ammonia, it is insoluble in acids. To the bromide precipitate add a solution of what is generally known as hyposulphite of soda ; the pre- cipitate will dissolve completely. The other pre- cipitate may be treated with potassium cyanide, with a like result. Now to go back to the first experiment, when metallic sodium was added to water, so that an atom of sodium took the place of an atom of hydro- gen, forming NaOH instead of HOH. If the ex- cess of water be driven off by heating the solution, or if enough sodium be added to combine with all the water, a solid mass of sodium hydrate (caustic soda, NaOH) will be formed. If more sodium be added to this and the mixture be warmed, the other OXIDES. 25 hydrogen atom will be turned out by the sodium, thus HOH, then NaOH, then NaONa. This substance, NugO, is called “ oxide ” of sodium, and much resembles the hydrate or caustic soda in appearance. Now add some caustic soda solution to a little silver nitrate solution — by a “ little is meant from half an inch to an inch of liquid in a small test-tube or measuring glass. A light brown precipitate will sink to the bottom. This light brown substance is oxide of silver, or Ag20, and is put together in exactly the same way as oxide of sodium. H.O.H H.O.H Na.O.Na Ag.O.Ag Oxide of Sodium, Oxide of Silver. The silver compounds must be left for a little while and something must be said about the salts of iron, which are not quite so simple as those of silver. Tirst dissolve up a few of the green crystals of sul- phate of iron or ferrous sulphate, as it is more cor- rectly called. To some of this add a little caustic soda and watch what happens : a precipitate is formed, first white, then green, and ultimately brown. If this white precipitate could be kept from changing whilst it was dried and heated, you would get an oxide of iron — “ an oxide ” because there are more than one. This oxide would be FeO, one atom of iron (Fe) being capable of turning out both atoms 26 FERROUS AND FERRIC. of hydrogen from water, or replacing two atoms of silver, or two atoms of sodium, etc. The white pre- cipitate was ferrous hydrate. As iron is capable of taking the place of two atoms of sodium, you have so that ferrous hydrate is Fe(OH)2. When this hydrate is dried and heated, a particle or molecule of water splits off, leaving the oxide, FeO, thus: — In actual practice, however, you have seen that the white precipitate turned green and then brown. The ferrous hydrate was using the oxygen of the air to convert itself into another hydrate containing more OH, viz., Fe(OH)g. From this you see that iron can combine with either two or three OH’s, i.e.^ can take the place of either two or three atoms of hydrogen or silver or sodium, etc. Consequently, ferrous .iron is always hungry until it has got hold of the third OH, or whatever it may be. It is im- portant that you should understand this thoroughly, as it is the basis of the development of negatives. In the solution, after the addition of the caustic soda to the ferrous sulphate, you had essentially (neglecting the sodium and the sulphate) water, oxygen from the Fej NaOH NaOH OXIDIZING AND REDUCING. 27 air dissolved in the water, and a substance — ferrous hydrate — ready to pick up any OH that might be available. The oxygen is anxious to combine with hydrogen to form water, so that you have ferrous hydrate and oxygen with a particle of water between, like a duck and a hen over a worm. The water comes in half, as the metaphorical worm would do, the iron gets its OH (hydroxyl) and the oxygen gets its hydrogen, and everybody is satisfied, thus : — Fe(OH )2 HO Fe(OH), HO Any substance that is anxious to get hold of hydro- gen acts like oxygen in presence of water, or, to put it in different words, is an oxidizing agent. Chlorine and bromine, for example, behave in this manner. If you had added chlorine or bromine to the ferrous hydrate, it would have gone brown at once. The action would have been complicated, however, by the hydrochloric acid formed (see page 19) dissolving the hydrate to make ferric chloride, in the same way that sodium hydrate with hydrochloric acid produced sodium chloride. How see what happens when ferrous sulphate is added to a silver salt, say silver nitrate : a black precipitate is formed. The iron, as it were, says to the silver, “ You’ve got my HO 3 ; drop it ! ” And the silver has to drop it and become “ reduced ” to 28 COMBINING PKOPORTIONS. metallic silver, whilst the ferrous iron appropriates the NO3 to raise itself to the ferric state. It is quite clear, then, that an oxidizing agent is a substance that is anxious to take up hydrogen, and, vice versd, a reducing agent is a substance that is hungering after oxygen. Hydrogen itself is a very powerful reducing agent. With metallic salts, oxidation raises them further from the metallic state ; reduction robs them of whatever other sub- stance, such as chlorine or nitric acid (nitrate), they are combined with, and brings them back wholly or partly to the simple metallic condition. From the talk about ferrous and ferric salts, you have seen that chemical elements may combine in other proportions than one to one. Silver chloride contains one of silver to one of chlorine ; ferrous iron takes two of chlorine ; ferric iron, three of chlorine ; in platinic chloride there is one of platinum to four of chlorine, and there are other compounds with a higher proportion of chlorine still. For convenience in chemical shorthand, the number of atoms of hydrogen an element is capable of replacing is de- noted by dashes, thus : — Ag'Cr, Silver chloride. Fe"Cl2, Ferrous „ Fe"'Cl3, Ferric „ Pt^''Cl4, Platinic ,, Sulphuric acid has the composition represented in chemical shorthand as H2SO4, so that, as ferrous iron can replace two H’s, the composition of ferrous WATER OF CRYSTALLIZATION. 29 sulphate is reS 04 . The green crystals that you buy, or that would be obtained if you evaporated a solution of ferrous sulphate to a thick syrup and allowed it to crystallize, contain water, as do most crystals. In assuming the solid condition many substances crystallize in two or three different forms according to the amount of water their particles entangle. Ferrous sulphate carries down with it seven molecules of water, so that the formula for the green crystals is FeS 04 , 7 H 20 . This is important, as in making up percentage or other solutions this water has to be taken into account. For instance, suppose a ten per cent, solution of ferrous sulphate is required. Then FeS04(56 + 32 + 64)=152 7 H 2 O (2 + 16) =126 278 So that 278 parts of the crystals only contain 152 parts of ferrous sulphate. To calculate how much FeS 04 must actually be used, you make the proportion sum, is to as is to the amount required. 152 : 278 : : 10 : 278 X 10 + 152 = 18*3 parts as nearly as possible. multiplied divided gives by by A few words now about acids ! Several different acids have been mentioned, but they possess one feature in common ; they all contain hydrogen. Acids are salts of hydrogen. Hydrochloric acid 30 ACIDS. (HCl) is hydrogen chloride just as AgCl is silver chloride ; sulphuric acid being hydrogen sulphate. The last named acid contains two atoms of hydrogen, both of which can be replaced by a metal, and there are other acids, such as phosphoric acid (H3PO4), which contain more than two atoms of hydrogen. In the carbon or organic acids, such as citric or acetic acids, there are atoms of hydrogen that are not replaceable, and their formulae are liable to confuse the reader, but in the last chapter (which see) the hydrogens that can be displaced by iron or sodium or silver, etc., to form salts, are shown quite clearly. With hydrochloric acid, where there is only one hydrogen, the latter must be displaced entirely, but with sulphuric acid, where there are two hydrogens, you may have either one or both atoms replaced by a metal. Tor instance, there are two sodium sul- phates, thus : — H2SO4, Sulphuric Acid. NaHSO^, Acid Sodium Sulphate. NagSO^, Neutral or normal Sodium Sulphate. The salt in which only one of the hydrogens has been displaced has an acid character, as you would expect, and is called “ acid sodium sulphate.” You will understand from this that an “ acid ” salt means a salt in which the hydrogen is only partly displaced by metal. The term “ bi ” is used fre- quently instead of “ acid,” so that NaHS04 is gener- ally called sodium bi-sulphate. SULPHATE AND SULPHITE. 31 In salts that are derived from acids containing oxygen there is a possibility of reducing that oxy- gen. Sulphuric acid or a sulphate, for example, may be deprived of one or two atoms of oxygen, producing H2SO4, Sulphuric acid. HgSOg, Sulphurous acid. H2SO2, Hyposulphurous acid. Their sodium salts are hTa2SO^, Sodium sulphate. Na2S03, ,, sulphite. NaoS02, „ hyposulphite. This last salt is true sodium hyposulphite ; the photographer’s “ hypo ” is not hyposulphite of sodium, correctly speaking, but sodium thiosulphate, ^^”a2S203. From all this the reader will gather some idea of the way in which chemical compounds are named. The termination “-ide ” signifies a salt consisting of a metal united with another element, such as silver- chloride ; “-ate ” signifies a salt containing oxygen as well ; “-ite ” contains less oxygen than “-ate.” If “ hypo ” is put in front of the word, it means that the salt is below the “ -ite ” stage. The prefix “ per ” or “ hyper ” means above, so that a per- sulphate of sodium is richer in oxygen than sulphate of sodium. Ha\fing said so much about acids, it is necessary to devote a paragraph to alkalies. You have seen at the beginning of the chapter that caustic soda or 32 ALKALIES. sodium hydrate is water in which one atom of hydrogen has been replaced by one of sodium. Caustic potash, or potassium hydrate, is exactly similar, potassium (K) taking the place of sodium. Caustic potash and caustic soda dissolved in water possess a peculiar “ alkaline ” taste, turn litmus paper blue, and neutralize acids to form salts. An alkali, therefore, is a soluble hydrate. Nearly all hydrates and oxides, although not soluble in water, have an alkaline tendency, and possess some of the properties enumerated above. Ammonia, properly speaking, is a gas, not a liquid. It is formed of one atom of the element nitrogen, which constitutes four-fifths of the atmos- phere, combined with three atoms of hydrogen. This NH3 dissolves in water with avidity, forming NH3H2O or NH4OH. Eather curiously this is a powerful alkali, and closely resembles caustic potash or soda in its action. So much is this so that NH4 is called by one word, “ ammonium,” and NH4OH is ammonium hydrate. The liquid ammonia of the druggist then is a strong solution of ammonium hydrate. This “ ammonium ” forms salts exactly like sodium or potassium, producing ammonium chloride, NH4CI, ammonium sulphate (NH4)2S04, etc. As caustic potash, soda, and ammonia are such strong alkalies, when they unite with a weak acid their salts are alkaline. Carbonic acid is a weak acid and sodium carbonate is strongly alkaline. CARBONATES. 33 The bicarbonate, although it is theoretically an acid salt, is faintly alkaline. Carbonic acid, by the way, is formed whenever carbon (coke or charcoal) or any substance containing carbon is burnt in the air. Carbon (C) unites with two oxygens to make COo, and when this gas dissolves in water carbonic acid is formed. The term “ carbonic acid ” is from long usage generally applied to the CO 2 gas, but all the carbonates are formed from CO 2 dissolved in water, thus, H20,C02 or H2CO3, Carbonic acid. NaHCOg, Sodium bicarbonate. Na2C03, „ carbonate. Sodium carbonate is the compound used as an alkali in photography. It can be obtained perfectly dry, but the most convenient form is washing soda. The crystals of this material contain water in the same way that ferrous sulphate crystals contain water, the formula for washing soda being Na 2 CO 3 , 10 H 2 O. How HagCOg adds up to 106 (46 + 12 + 48) and 10 of water make 180; so that, adding the two together, 286 of washing soda are equivalent to 180 of dry sodium carbonate, and this fact must be borne in mind when making up solutions. This is a convenient place to say a few words about electro-chemistry. When two metals, such as zinc and copper, are joined together and placed in a liquid that conducts electricity, such as dilute c 34 ELECTRO-CHEMISTRY. sulphuric acid, an electrical current is produced and flows from the copper or positive metal through the wire, or whatever it is that joins them, to the zinc or negative metal, then through the acid back to the copper again, completing the circuit. This arrangement is called an electric battery ; various other combinations of metals are used in different batteries, but the principle is the same. It is not necessary to use two metals to produce an electric current, a metal and a solution of a metallic salt, or even two solutions separated by a porous parti- tion, being sufficient to cause a current. It is evident that nearly every chemical change must produce an electric current or vice versd, and it is difficult, if not impossible, to separate one from the other. Now try this experiment : Make a little electric battery of a strip of zinc and a strip of some other metal, dipping in dilute acid in a jam-pot or some- thing of the kind ; connect the copper strip by a wire to another smaller strip of copper, and the zinc in a similar way to another little strip of zinc ; allow the two latter strips to dip into a solution of sulphate of copper in a beaker or glass of some kind, so that you can see what is going on. In a few minutes, the zinc strip will have become coated with copper, and if you had weighed the copper strip before the experiment you would find that some of it had dissolved. This is the principle of electro-typing, electro-plating, electro-gilding, and ELECTRO-DEPOSITION. 35 so on. If you had had a convenient solution of silver instead of the sulphate of copper, silver would have been deposited on the zinc. As you will see in the next chapter, much of what goes on during development resembles electro- plating. In the solution a kind of “ ladies’-chain ” is taking place, the atoms of metal travelling in the direction of the current, to be deposited finally on the negative electrode or terminal of the wire con- nected with the zinc of the battery or what corre- sponds to it. In developing, it is very possible that each particle of reduced silver in the latent image acts as the terminal of a tiny electric battery or couple ” as it is called, and the silver from the sur- rounding silver salts is deposited on it to build up the visible image. 36 PHOTO-SALTS. CHAPTEE III. The Chemistry of the Photographic Image. The chemistry of the different processes for pro- ducing and developing a latent image are so inter- woven that it is convenient to talk about them to- gether ; the composition of the different plates and developing materials will be considered separately afterwards. First of all, however, it will be necessary to say a few words about the photo- chlorides and kindred salts of silver. The photo-chlorides of silver, which Carey Lea did so much to investigate, are the compounds pro- duced by the action of light or reducing agents, such as ferrous sulphate, on silver chloride. They con- tain less chlorine than silver chloride, and may be regarded as stepping-stones between silver chloride and metallic silver. There seems to be a consider- able number of them, and they vary in colour from white, through flesh-colour, pink, rose, copper-red, reddish-purple and chocolate, to black. They appear to be permanent if kept in the dark, but change rapidly in the light. More about these interesting THERMOGRAPHIC IMAGES. 37 compounds and about some curious and beautiful forms of metallic silver, which are soluble in water, will be found in chapter VII. The photo-bromides and photo-iodides resemble the photo-chlorides very closely. In all cases the presence of soluble chlorides, bromides or iodides, such as sodium chloride or potassium bromide, etc., in solution hinders the formation of the photo-salts, an acid having the same effect, whilst an alkali or reduced silver hastens their formation. To pick up the thread where it was dropped at the end of the last chapter. Hunt found, in the early days of photography, that invisible images could be produced by heat, and that these could be developed subsequently. If a hot coin be held close to a piece of clean glass, the image of the coin can often be reproduced by breathing on the glass. The action is probably electrical, but in any case there is a selective action, so that the moisture sticks to one part and not to another. Hunt used polished metal and developed his images with mercury vapour, the principle being the, same. In Daguerre’s process a polished silver plate was exposed to iodine vapour, so as to form a thin film of silver iodide on the surface. This plate was then exposed in the camera, and developed with mercury vapour. In this case the result was very different from the heat or “ thermographic ” images. The light in the bright parts of the image thrown by the lens had reduced the silver iodide in the thin 38 DAGUEEKEOTYPK film on the surface, and the liberated iodine probably acted on the metallic silver just behind to form more photo-iodide, thus intensifying the effect of the light. The mercury vapour combined chemically with the reduced parts of the plate, so that a visible image was formed. This was fixed and toned with gold salts. So far you have seen, first, a mechanical effect caused by beat, and developed mechanically; secondly, mechanical effect, caused by light, ending in chemical action, and extended or developed by chemical action. In the former case the invisible or latent image was due probably to different electrical conditions on different parts of the surface. In the latter case, you have every reason to suppose that the latent image was composed of reduced silver iodide or photo-iodide. I should like to take the opportunity here of impressing on the reader’s mind the fact that photographic action is not yet thoroughly understood. Even in such a comparatively simple affair as a Daguerreotype plate, the latent image cannot be taken out and examined. In wet plates, and more especially dry plates, the conditions are much more complicated, so that the difficulty in finding out what happens is greatly increased. Consequently, scientific guesswork has to be brought to the aid of the investigator ; the guesswork is of a very shrewd order, but it is guesswork none the less. When you consider that in a wet plate, for example, you have an almost microscopically thin, THE LATENT IMAGE. 39 and by no means simple, film to start with, and that only the outermost particles of this thin film appear to be affected directly by the light, you will see that it is not easy to lay down the law as to what happens in the film. A wet plate after exposure consists essentially of a film of collodion containing silver iodide, a part of which has been acted upon by the light, and this is covered with a layer of silver nitrate. The developer, made up of a solution of ferrous sulphate containing a little acid — generally acetic acid — is poured over this. Ferrous sulphate alone would reduce the silver nitrate at once, covering the plate with a black deposit of metallic silver ; but the presence of the acid hinders this action, so that the reduction only proceeds slowly. Probably the first action of the developer is to reduce to the metallic state the photo-iodide that has already been acted upon by the light. This forms a nucleus for the deposit of silver from the reduced nitrate, in a similar manner to the selective action in the thermographic image, and this reduced silver is built up on the latent image forming the visible image of the wet plate. As development proceeds the ferrous sulphate becomes oxidized (see p. 27 ) and loses its reducing power, so that the formation of the image progresses more and more slowly, or in photographic language, the developer becomes more and more restrained. It is obvious that if any substance be present that will absorb the acid given off by the silver on reduc- 40 poitevin’s experiment. tion the formation of the image will go on more rapidly. In 1866 Poitevin tried the experiment of squeezing a collodion film containing silver iodide, free from excess of nitrate, on to a silver plate, and treating a glass plate in a similar manner. Both were exposed to light and developed. The film on the silver plate showed a considerable image, being very much denser than that on the glass plate, but the latter did show a slight image. Prom this it is clear that an image of reduced silver can be formed even when there is nothing to absorb the iodine or whatever it may be that is given off. It is con- jectured that in such a case a compound must be produced similar to KI 3 — the dark substance obtained on dissolving iodine in potassium iodide. The statement that an absorbent of iodine, chlorine, or acids, such as metallic silver, hastens development, however, is amply proved by this experiment. In making a wet plate for use, collodion (see chap. XIV.) is iodized by dissolving soluble iodides or even iodine itself in the collodion. Except for process work, it is usual to employ bromide as well as iodide. The latter alone gives a hard negative, and bromide alone a flat detailed negative ; the proportion of the two can be varied to suit the subject. The bromides and iodides of cadmium and ammonium are those generally used. The glass plates to be coated must be carefully cleaned and polished with tripoli, whiting, or rouge, or better, by soaking in sulphuric acid and bi- PREP A KING WET PLATES. 41 chromate of potash (see p. 14) ; then edged with india-ruhber solution and given a first coat or sub- stratum of albumin or gelatin to which a few drops of ammonia have been added. This preliminary edging and coating is to prevent the collodion slipping or coming away from the glass. The iodized collodion is poured on to the plate and distributed evenly by rocking, the excess being drained off at one corner. In subsequent opera- tions this corner should always be kept at the bottom. The plate is then immersed in a bath of silver nitrate which is generally made faintly acid with nitric acid. The silver nitrate is converted into bromide and iodide (see p. 22) and the plate is ready for use. As this iodide is soluble in silver nitrate, the silver bath is saturated with iodide before use by adding a few grains of potassium iodide, and filtering ofi' any undissolved precipitate of silver iodide. After exposure the plate is developed by pouring over it a solution of ferrous sulphate made acid with acetic acid. Ammonio-ferrous sulphate and copper sulphate are used sometimes in the de- veloper; the former replaces part of the ferrous sulphate, acting more slowly, and the latter acts as a restrainer. The positives on glass, made by the wet plate process, are really negatives which receive a less exposure in the camera than is required for the ordinary negative, and are coated on the film side 42 FORMULA FOR WET PLATES. with black varnish after development. Conse- quently the black of the varnish shows through the transparent parts of the plate, and the silver deposit shows white by reflection, so that the nega- tive is turned into a positive. The various formulae for producing a flnished wet plate negative are as follows, those marked with an asterisk being employed at the Bolt Court Process School : — The Substratum.^ Sheet gelatin, . 2*5 grams, . 22 grs. Ammonia '880, . . 4 c.c., . 40 minims. Water (distilled), . 1000 c.c., . 20 fl. ozs. Rubber Solution for Edging,"^ Pure rubber cut into small pieces, 1 gram, . 20 grs. Benzole, .... 100 c.c., . 5 ozs. Silver Bath for Sensitizing.^ Silver nitrate, . . 68 grams, . 600 grains. Water (distilled), . 1000 c.c., . 20 fl. ozs. Pot. iodide (10% solution), 1 c.c., . 60 minims. Sodium carbonate cryst., 3'5 c.c., . 30 grs. Dissolve the silver nitrate in one-quarter of the total water, then add the potassium iodide, and shake ; when the precipitate has dissolved add the sodium carbonate dissolved in part of the water, shake, and add the rest of the water. Acidify with a few drops of 107 o nitric acid. COLLODION FORMULAE. 43 Collodion,'^ Plain collodion, . , 750 c.c., . 15 ozs. lodizer (B. solution), . 250 c.c., . 5 ozs. 1 lodizer {B, Solution). Iodine, . . *45 gram, . . .2 grs. Alcohol (ethyl), 100 c.c., . . . 1 oz. The iodizer must be mixed with the collodion in the proportion given, at least 24 hours before use. Store in a cool place, and do not disturb the sediment. Collodion {another Formula). Plain collodion, . 100 c.c., . Cadmium iodide, . *1 gram. Ammonium iodide, ‘7 ,, Ammonium bromide, *4 „ 1 oz. J grain. 3 grains. 1 2 ^3 The iodides and bromide may be dissolved in the collodion, which is then suitable for general purposes. The proportions can be varied to suit the subject in accordance with the following tables, remembering that cadmium has a tendency to make the collodion granular. The table of chlorides is added for convenience. 44 BROMIDE AND IODIDE EQUIVALENTS. TABLE IV. — Equivalent Quantities of Different Bromides. Bromine. Am- monium Bromide. Potassium Bromide. Sodium Bromide. Cadmium Bromide + 4 H 2 O. Zinc Bromide. Silver Bromide. 1 1-225 1-488 1-287 2-150 1-406 2-350 0-816 1 1-214 1-055 1-754 1-147 1-918 0-672 0-823 1 0-865 1-445 0-945 1-579 0-777 0-952 1-156 1 1-671 1-092 1-8-26 0-465 0-570 0-692 0-599 1 0-654 1-092 0-711 0-871 1-058 0-915 1-529 1 1-670 0-422 0-521 0-633 0-548 0-914 0-600 1 TABLE V. — Equivalent Quantities of Different Iodides. Iodine. Am- monium Iodide. Potassium Iodide. Sodium Iodide. Cadmium Iodide. Zinc Iodide. Silver Iodide. 1 1-142 1-307 1-181 1-441 1-255 1-853 0-876 1 1-145 1-035 1-262 1-099 1-624 0-765 0-874 1 0-903 1-102 0-960 1-418 0-847 0-967 1-107 1 1-220 1-063 1 -570 0-694 0-793 0-907 0-820 1 0-871 1-286 0-797 0-910 1-042 0-941 1-148 1 1-477 0-539 0-599 0-706 0-637 0-777 0-678 1 WET PLATE DEVELOPERS. 45 TABLE VI. — Equivalent Quantities of Different Chlorides. Ciiloiine Ammonium Chloride. Sodium Chloride. Potassium Chloride. Cadmium Chloride. Silver Chloride. 1 1-507 1*648 2-101 2*575 4*042 0*663 1 1-093 1*394 1*710 2-682 0*607 0*914 1 1-275 1-564 2-453 0-475 0-717 0*784 1 1*226 1 * 9-23 0-388 0-584 0*639 0-818 1 1*570 0*247 0*373 0*408 0-520 0*630 1 If the collodion becomes too thick it may be “ thinned ” by adding a little of a mixture of 2 parts ether (*730) to 1 part alchohol (*805). In the wet plate process methylated alcohol and ether must not be used on any account. Developing Solution for Negatives.'^' Ferrous sulphate, 34 ‘5 grams, . 300 grains. Acetic acid glacial, 52 c.c., . 500 minims. Eectified spirit, . 31 ,, . 300 ,, Water (distilled), 1000 „ . 20 ozs. Developing Solution for Positives, Pyrogallic acid, 25 grams, . Acetic acid, . 4 c.c.. Alcohol, . 5 ,, Water, 100 „ 5 grains. 100 minims. 120 „ 5 ozs. Fixing Solutions. A. Potassium cyanide, . 50 grams, . 1 oz. Water, . . . 1000 c.c., . . 20 ozs. Take care that the cyanide is fresh. 46 DRY PLATES. B. Sodium thiosulphate (hypo), 200 grams, 4 ozs. Water, .... 1000 c.c., . 20 ozs. Either A. or B. may be used. For intensification and reduction see chap. VI. j Further information about the wet plate process | will be found in Wet Collodion Photography ^ byj Charles W. Gamble. I The dry plate differs from the wet plate in many important respects. Silver bromide and a little! iodide, or rather the materials to produce these—' silver nitrate and potassium or ammonium bromide and iodide — are incorporated . in an emulsion of • gelatin, which is spread on glass plates or some other stiff material, such as celluloid, and allowed to dry. Collodion is sometimes employed instead of gelatin ; the first dry plates having been made of collodion emulsion before gelatin was thought of. Before coating the plates, all excess of potassium and ammonium bromides and iodides, etc., are removed from the emulsion by prolonged soaking in water, the sensitiveness of the plate depending to a large extent on the thorough removal of these salts. After exposure to light in the camera quite a different state of things exists to that on the wet plate. The silver salt (bromide mostly) is im- bedded in gelatin, and is, therefore, much less open to attack by the developer, and there is no silver nitrate present. Two consequences arise from this : The silver image cannot be built up above the ACTION OF THE GELATIN. 47 latent image, as in the absence of silver nitrate there is no material to build from, so that the image must be formed from the silver bromide in the emulsion; moreover, the silver image is sunk downwards into the film instead of being built up above the latent image. Secondly, as no easily reducible silver salt is present, much more powerful developers or reducing agents can be used than sulphate of iron or other ferrous salts. Although a further reference will be made to gelatin in the chapter on developers, in connection with pyrogallic acid, etc., a few words here about the complications introduced by the gelatin will not be amiss. In the first place, gelatin is a most complicated body itself, containing carbon, hydro- gen, nitrogen, and oxygen, and its chemical structure is not known, so that when other substances, such as silver bromide, are mixed with it, complicating matters still further, it is not easy to find out exactly what happens. Either the silver bromide, before exposure, may lie perfectly inert, like so much shot in the gelatin, or it may combine bodily with the gelatin, or some interchange may take place between them; the combination, if it exists, is probably a loose one. In any case the ultimate effect is to allow the silver bromide to present a large surface to the action of the light. The pro- cess of stewing the emulsion or mixing ammonia with it, both of which have such a strong effect in adding to the sensitiveness of the plate, probably 48 THE BUILDING OF THE IMAGE. act by causing a most intimate mixture of silver bromide and gelatin. When the plate is exposed, and still more when it is developed, the gelatin probably increases the sensitiveness by absorbing the free bromine when the bromide is reduced, in the same way that the metallic silver acted in Poitevin’s experiment. It is a doubtful point whether the silver bromide that has not been touched by the light, as, for example, the deeper parts of the film in an under- exposed plate, can be reduced by the developer, so as to help in building up the image. As the reader prob- ably knows from bitter experience, the shadows and detail in the half-tones of a badly under-exposed plate remain absolutely unreduced, even after pro- longed development. On the other hand, Abney tried the experiment of exposing a gelatino-bromide plate in the camera and then covering it with a collodio-bromide emulsion. On development, the two films were separated, and it was found that each contained an image, so that whilst the image was developing downwards in the ordinary way in the gelatino-bromide film, it was being added to from above by the silver bromide in the superposed film that had never seen the light. This result was confirmed by an experiment of Eder’s, who suc- ceeded in developing the image completely through a very thick and opaque film. When something is known with certainty about the nature of the latent image, it will be possible perhaps to say what is the correct view. COLLODION DRY PLATES. 49 A collodion dry plate is made as follows ; — Alcohol ('820), Ether (-730), . B. Zinc bromide, Alcohol, Nitric acid, C. The same as B. D. Silver nitrate, . Water (warm). Alcohol (warm). Nitric acid. Add the alcohol after the 40 grains. 1 oz. 2 ozs. 3 grams, . 40 grains. 1 C.C., or sufficient to dis- solve the solid. 2 drops, . 2 drops. 9 grams, . 130 grains. 7 or 8 C.C., ^ oz. 20 C.C., . I oz. 4 drops, . 4 drops. crystals have dissolved, A, Pyroxyline (see p. 128), 3 grams, 30 C.C., 60 C.C., and mix thoroughly. When all is ready put A in a wide-mouthed bottle sufficient to contain the whole ; add B, and shake round. To the mixture add two-thirds of D, shaking round the while ; then the whole of C, still shaking or stirring ; then the remainder of D. The emulsion may be used as it is or washed. When the plate, which must be edged with rubber as described in the wet plate process, has been coated by pouring the emulsion in a puddle in the middle, and making it flow all over the surface by tilting, it is allowed a few seconds to set and is then washed by pouring water over it. This removes any soluble salts and renders the emulsion more sensitive. Any weak developer (1 grain of pyro. to the oz. for example) may be used with these plates, and they may be fixed with potassium cyanide or sodium D 50 GELATINO-BROMIDE EMULSION. thiosulphate (hypo), as given for wet plates, prefer- ably the former. The plates should be under- developed, as compared with gelatine dry plates, and then intensified (see chap. VI.). There are numerous formulae for making gelatine dry plates, and the proportions of bromide and iodide vary according to the object for which the plates are intended to he used. The following formula,^ due to E. Child Bayley, may be taken as an example of a gelatine bromo-iodide emulsion. A. Potassium bromide, . 43 grams, IJ ozs. Distilled water up to . 300 c.c., . 10 „ B. Silver nitrate, re-crystallized, 52 grams, If ,, Distilled water up to . 360 c.c., . 13 „ C. Potassium iodide, . . 1*6 grams, 25 grains. Distilled water up to . 60 c.c., . 2 ozs. The proportions in these stock solutions are sufficient to make twelve batches of emulsion of half-a-pint each. Solution B should be rendered faintly acid to litmus paper by adding two or three drops — not more — of acetic or nitric acid. For use take A. 75 c.c. (If ozs.) containing 10*75 grams of potassium bromide. B. 90 c.c. (3f ozs.) containing 13 grams of silver nitrate. C. 15 c.c. (5 drams) containing 0*4 grammes of potassium iodide. * A full account of emulsion making, from which this formula is taken, will be found in Vol. II. of The Photograin, p.l52. Other formulae, varied to suit the most exacting tastes, will be found in the different year books of the photographic journals. MAKING THE EMULSION. 51 A is placed in a large (20 oz.) flask, B in a smaller flask. Two grammes of hard (Heinrich’s) gelatine are weighed out and allowed to soak for an hour in the cold bromide solution in the larger flask. Both flasks are brought to 160° F. by placing in a saucepan half full of hot water, and testing with a thermometer. The contents of the smaller flask are then added in smaller quantities at a time to the gelatine and bromide in the larger flask, shaking the while. When the whole mixture is made C is added, and the emulsion is placed in a covered earthenware jar to stew in the saucepan for an hour or so. The jar is supported by passing through a tin plate on the top of the saucepan, so that the bottom of the jar is about an inch from the bottom of the saucepan. At this point the emulsion should be tested by placing a drop on a piece of clean glass, taking it out of the dark room, where all the operations, except the weighing and making up of the stock solutions are conducted, and looking through it at a candle flaine. The emulsion should not appear gritty or strongly coloured. After stewing in water, boiling gently for an hour or so, until it appears almost blue on examining a drop by the candle flame, the emulsion is allowed to cool, 10 grams more gelatin, which have been soaking in cold water for an hour, are added, and the whole well stirred until dissolved, when it is allowed to set. The cold emulsion is washed to soak out any soluble bromide, iodide, and nitrates, by squeezing it 52 COATING THE PLATE. many times through net or canvas under water. The emulsion is then warmed to 120° F., when the following is added, a few drops at a time, and the whole filtered through calico or chamois leather : — Chrome alum (1 per cent, solution), 10 c.c., 3 drams. Alcohol, . . . . . 40 C.C., IJ ozs. The plates to be coated must be cleaned thor- oughly by washing with strong soda, rinsing well, and allowing to dry. It does not pay as a rule to re -coat old negative glass. The coating may be performed with emulsion warmed up again to 105° F., in a somewhat similar manner to that described under wet plates. More material, however, must be run on to the plate, and very little need be drained off. The plate is rocked for some time, and then placed on a carefully levelled piece of glass to set. Drying must be performed in a dark room, or well- ventilated cupboard as free as possible from dust. Kote. — Never 'pack plates in newspaper under any circumstances, as the print will be reproduced on development. Grooved cardboard boxes form the best packing. STANDARD IRON DEVELOPER. 53 CHAPTER IV. Developers. By this time the reader understands a good deal about the general principles of development. So far, however, acid iron developers only have been talked about. In a gelatin dry plate there is no easily reducible silver nitrate present, and the silver bromide itself is protected to some extent by the gelatin, so that much more powerful developers can be used than with wet plates, and alkalies can be introduced, which adds greatly to the rapidity of the plates. The acid iron developer is very suitable for gelatin plates, giving very vigorous negatives, al- though it is necessary for the exposure to be cor- rectly made. This developer is used in most standard work as it causes no stain in the film. The following is the standard formula used in speed- testing on the Hurter and Driffield system, which will be referred to again directly. The formula, which works excellently, is due to Mr Cadett. Ferrous oxalate is the iron salt used as a reducing 54 STANDARD IRON DEVELOPER. agent ; instead of the oxalate itself, however, the materials for making the oxalate, namely ferrous sulphate and potassium oxalate, are employed. Ferrous Potassium Ferrous Potassium Sulphate. Oxalate. Oxalate. Sulphate. FeSO^ + K2C.2O4 = FeCgO^ + The potassium sulphate produced does not inter- fere with the development. Ferrous Oxalate Formula. A. JNeutral oxalate of potassium, 200 grams, 1 part. Distilled water, B. Sulphate of iron. Citric acid, Distilled water, C. Potassium bromide, Distilled water. . 800 C.C., . 4 parts. . 100 grams, 1 part. 1 gram, „ 300 C.C., . 3 parts, 1 gram, 1 part. . 100 C.C., 100 parts. For test use take A, 100 parts ; B, 25 parts ; C, 10 parts, in the order named. Make the devel- oper up to a temperature of 65° F. and develop for live minutes ; then, without washing, fix in a bath of sodium thiosulphate (hypo) made up of 1 part to 3 parts of water ; then after thorough washing, place the plate in a 2°/^ solution of hydrochloric acid to remove lime or other stains, and finally wash well. The addition of a few drops of 1% sodium thio- sulphate (hypo) solution to each ounce accelerates the development of under-exposed plates when using INFLUENCE OF TEMPERATURE. 55 a ferrous oxalate developer. The exact action is not known. When using the above formula for ordinary studio or landscape work, it is a convenient plan to commence development with an old developer. This contains bromide from the reduction of the silver bromide in the film, so that there is no occasion to add bromide when working with an old developer. Many photographers stand the bottle containing the old developer in the sun to re- generate it, the light reducing the ferric oxalate to ferrous oxalate, which can be used over again. Ferric oxalate. Ferrous oxalate. Carbonic acid. Fe2(C20^)3 + light = 2FeC20^ + 2COo. In the directions given above for using the ferrous oxalate developer, the correct temperature for development was stated to be 65° F. For standard work, such as testing the speed of plates, it is necessary to have the temperature as uniform as possible, and even in ordinary work, although ex- cessive accuracy need not be observed, it is well to always develop as far as possible at the same temperature. Many photographers know the im- portance of employing a thermometer, but many others fail to realize the marked effect increase of temperature produces in hastening development. In some experiments made recently by the author, a difference of 15° — from 55° to 70° F. — -caused an increase in the density of about one-third. From i 56 EESTRAINERS. this it is clear that an under-exposed plate should be developed with a warm developer at, say, 70° F, and an over-exposed plate with a cold developer at, say, 45° to 55° F. This is a convenient stage to talk about restrainers. It was seen (p. 37) that all soluble haloid salts (chlorides, bromides, and iodides) had a tendency to hinder the reduction of the bromide and kindred salts of silver. Their principal action is to form a double salt, which is more soluble than silver bromide, so that potassium bromide in the developer always dissolves silver bromide out of the film. This double salt is much less easily broken up by the reducing agent, so that the action is much slower. As any soluble haloid can be used, common salt may be used as a restrainer in the absence of potassium bromide. The reason why acids act as restrainers was ex- plained on page 40. It is advisable to always work with some bromide in the developer, as other- wise the image comes up much too quickly and the silver is apt to be reduced to a greater or lesser extent over the whole plate, causing “ fog ” and obscuring the finer detail. All the organic developers in general use bear a close chemical resemblance. Phenol (carbolic acid) is the base of them all, and phenol itself is benzene in which one hydroxyl (OH) has taken the place of one atom of hydrogen. Benzene, CgHg, is always represented in chemistry like this. PYROCATECHIN, RESORCIN, HYDROQUINONE. 57 H 1 H 1 1 C (i H— C C— H H— C C— OH 1 1 phenol being 1 1 H-C C— H H— C C— H V \/ c 1 C 1 1 H 1 H Pyrocatechin, resorcin, and hydroqninone are di- phenols, i.e.^ they contain two OH’s, OH 1 OH 1 OH 1 C c c H— C C— OH 1 1 H— C C— H H-C C-H 1 1 1 1 H— C C— H 1 1 H— C C— OH 1 1 H_C C— H V V V C 1 C 1 C 1 H 1 H H Pyrocatechin. Resorcin. Hydroquinone, 1-2 1-3 1-4 the difference being that the atoms are arranged differently, all three compounds having the formula (OH),. Pyrogallic acid is a tri-phenol, having the formula 06113 ( 011 ) 3 , and is still the most extensively used of all developers. It is very soluble in water, 58 ACTION OF SULPHITES. forming a 40 per cent, solution when saturated. It is soluble also in alcohol, ether, and glycerine. Like phenol (carbolic acid), it is not a true acid, such as sulphuric acid, and its proper chemical name is pyrogallol. It does form a combination with alkalies, however, and in this condition is a very powerful reducing agent. If left exposed to the air, it absorbs oxygen rapidly, turning first yellow, then brown, and finally black. The exact nature of the oxidation compounds formed are not accurately known. These brown products have a strong staining action on the gelatin so that under-exposed negatives are much more liable to be stained as, not only are they in the developer for a much longer time, but the pyrogallate (i.e., the compound of the pyrogallic acid with the alkali) is much more highly oxidised through contact with the air all the while. It has been found that a sulphite has the power of pre- venting this staining to a large extent. Sulphite of soda, Na2S203, is generally employed, but sometimes the metabisulphite of potassium (K2S2O5) takes its place. The drawback to the last-named is that it renders the solution very acid after a short time. Only one quarter the amount of metabisulphite is required, as compared with the crystallized sulphite. As regards the influence of the quantity of sul- phite in the developer on the resulting negative, sulphite has a distinct restraining action on the actual deposit of silver, and if a very large propor- tion of sulphite be present the developer almost PYRO-STAIN. 59 stops working. The diminution of the yellow stain in the negative, howeyer, is very marked as the sulphite is increased. The reduction in the quantity of sulphite from 5 to grains to the fluid ounce of developer, in some recent experiments by the author doubled the yellow stain in the dense part of the experimental plate, and increased it by about four times in the lighter portions. The entire absence of sulphite in another part of the same plate caused three times the stain in the denser parts, and about five times in the lighter parts, as compared with that portion of the plate developed with 5 grains to the oz. Alfred Watkins and others have shown that this “ pyro-stain ” has an important influence on the printing value of the negative, so that it is better to use sufficient sulphite, say 3 grams to the 100 c.c. or 15 grains to the oz., to practically elimin- ate the staining altogether. Some photographers have an affection for the yellow stain, and think it improves the “ quality ” of the negative. This may be true in cases of hard negatives, but the photographer should have complete command of his plate in the same way that the engine-driver has of the various levers that control the engine. If stain- ing is allowed to creep in, the result becomes largely a matter of chance. For the same reason, the photo- grapher should understand the effect of, and have under his command, each separate constituent of his developer, for these are the levers, so to speak, that control the photographic negative. 60 ALKALIES IN DEVELOPMENT. Ammonia solution or the carbonate of sodium and potassium are the alkalis employed in develop- ing with pyrogallic acid. Ammonia, although it is still largely used, especially by professional portrait photographers, seems unsatisfactory, because the ammonia evaporates from the solution during development, so that the developer grows continually weaker in alkali ; the original concentrated solution itself is always varying in strength. Besides this, it must be a very bad thing for other plates or sensitive material to be in a room reeking with fumes of ammonia, which combine with any acid fumes that may be about, and deposit over every- thing in minute crystals. Potassium carbonate possesses no advantage over sodium carbonate except that it is much more soluble, which is an advantage in making up very strong solutions, but has the drawbacks that it is much dearer, is more difficult to obtain, and more of it is required in the developer. Sodium carbonate is the most convenient alkali to use. Ordinary washing soda is the form generally employed, but there are two other forms that can be used equally well, namely, the monohydrated sodium carbonate and dry powdered sodium carbonate. The former of these two has recently been introduced commercially so that it is well to include it. The latter is, or should be, pure sodium carbonate, NagCOg. The following table gives the equivalence of the three carbonates to one another CAKBONATES OF SODA. 61 and to sodium hydrate (caustic soda), which may be useful with other developers. TABLE YIII. — Equivalence between Caustic Soda AND Carbonates of Soda. Dry Sodium Carbonate. Monohydrated Sodium Carbonate. Washing Soda. Caustic Soda. 1 1-17 2-70 0-76 0-85 1 2-30 0-64 0-37 0-43 1 0-28 1*32 1*55 3-35 i 1 ! It is convenient to know that bicarbonate can be converted into normal (dry) carbonate of sodium by heating it strongly, or by boiling its solution for some time. Sixteen parts of the bicarbonate are equiva- lent to ten parts of the ordinary dry carbonate. Increase of alkali has a strong effect in hastening the rate of development all over the plate, excess causing fog. Variations in the quantity of the pyrogallic acid itself are important. It must be remembered that excess of pyrogallic acid acts as a restrainer unless the alkali is increased in the same proportion. In some recent experiments the author has found that the greatest density was obtained with the pyrogallic acid and alkali in proper chemical proportion (2 grains “ pyro ” to 7 grains washing soda). Half this quantity of pyro (1 grain to the ounce), the alkali 62 VARYING THE PYROGALLOL. remaining the same, gave less than half the density in the high lights of the negative, and only one- fifth or one-sixth in the shadows. When the pyro was increased by a half {i.e., to 3 grains) there was a distinct falling-off in the density, as compared with the rightly proportioned developer, to three- quarters in the high lights, and about the same in the shadows. When the pyro. was doubled (i.e.,4: grains to the ounce) without change in the alkali, the result was practically the same as if one grain to the ounce had been used, showing the strong restraining action of the pyrogallic acid. As the shadows were restrained more in proportion than the high lights, a considerable excess of “ pyro ” over alkali is clearly an advantage in developing an over- exposed plate. The effect of bromide in this direction, however, is almost the same. With these experiments in varying the quantity of pyrogallic acid in the developer, it was found that the yellow stain did not increase with the “ pyro ” by any means, appearing to bear little relation to it, but followed the density of the silver deposit very closely. As regards the composition of the developer, every photographer must be a law unto himself. The developer must be handled according to the exposure of the plate and the result the worker desires to obtain. The formulae given by plate makers are, as a rule, needlessly complicated. The following is a good, sensible formula, which will work well with any plate. PYROGALLIC ACID DEVELOPER. 63 Pyrogallic acid, . . ‘5 gram, Sodium sulphite (crystals), 4’0 „ Sodium carbonate (crystals), 1’5 ,, Potassium bromide, . . '25 „ Water up to . . .100 c.c., 2 20 7 1 1 grains. jj j) oz. Unless a large number of negatives are to be developed, it is much better to use dry pyrogallic acid, weighing out sufficient for each small batch of plates before commencing development, and making it into a ten per cent, solution. The other materials may also be used conveniently in the form of ten per cent, solutions. The quantities to be taken to make up the above developer would be : — Pyrogallic acid 10%, . 5 c.c.. . 20 minims. Sodium sulphite 10%, . 40 „ . 160 55 Sodium carbonate 10%, . 15 „ . 70 55 Potassium bromide 10°/^, 2| „ . 10 55 Water up to . 100 „ 1 OZ. It is convenient, as a rule, to add half the alkali at the beginning and the remaining half as ex- perience dictates. If the sky and high lights appear to be growing too dense, the full quantity, and even an excess, of alkali should be added immediately. In the following formula ammonia takes the place of sodium carbonate, ammonium bromide being used instead of potassium bromide. Pyrogallic acid, . . *25 gram, Sodium sulphite, . P2 „ Ammonium hydrate, ( Liquor ammonise '880) j Ammonium bromide, ’25 gram, Water up to . . 100 c.c., 1 grain. 2*5 minims. 1 grain. 1 oz. 64 STOCK SOLUTIONS. Ten per cent, solutions may be used as recom- mended in the previous formula. When large quantities are required, the sulphite and the pyro- gallic acid may be incorporated into one stock solution in the proportion of — Pyrogallic acid, 50 grains, . . 1 oz. (avoir.). Sodium sulphite, 250 „ . • 5 ,, „ Water up to . 1000 c.c., • 20 „ „ For use take 20 minims of the stock, 4 drams of 10°/o ammonia, and 10 minims of 10% ammonium bromide with water to make up one ounce. If a stronger developer is required, all the constituents may be increased in the same proportion. Nearly all the remarks made in connection with the sodium carbonate developer apply to the one just recorded. When making up stock solutions of pyrogallic acid, ferrous sulphate, or any easily oxidizable materials, it is a good plan to use the arrangement figured on page 65, whether a burette is employed or not. But, as every time a quantity of liquid is drawn off from the large containing vessel the same volume of air enters, it is necessary to put in an oxygen trap, as shown in fig. 5. Either a small bottle can be used or a glass bulb intended for the purpose can be purchased at a chemical dealer’s. The bottle or bulb contains an inch or so of strong pyrogallic acid and soda in the OXYGEN TRAPS. 65 same proportions as used in the developer ; this arrangement will last for a year or more without being renewed. If the oxygen trap, etc., is not available do not put the whole stock into one stoppered bottle, as is generally recommended ; but fill a number of small corked bottles with the solution, cork them tightly, melt up some paraffin candle ends in an iron ladle or something of the kind, and dip the tops of the bottles in the melted paraffin to render them air-tight. Stock solution treated like this will keep indefinitely, and no preservative, such as citric acid, is required, as there is no large air space above the solution to make it go wrong. E 66 HYDKOQUINONE. Hydroquinone works more slowly than pyrogallic acid. For that reason there is less tendency to fog the plate during the prolonged development necessary for under-exposed plates, for which hydro- quinone developer is very suitable. Although an excellent developer, there does not seem to be so much control over the plate as with pyrogallic acid. The following is a good formula, giving a choice of either sodium hydrate or carbonate ; the former is to be preferred. Except in cases of over-ex- posure for which hydroquinone is not satisfactory, the bromide may be left out. Hydroquinone, . . . *8 gram, . 4 grains. Sodium sulphite (crystals), 3‘5 „ .16 „ Citric acid, . . . . '05 „ . | „ Potassium bromide, . . '2 „ . 1 „ f Caustic soda, . . . '4 „ . 2 „ 4 or [ Sodium carbonate (crystals), 3*0 „ .15 „ Water up to . . 100 c.c., . 1 oz. Caustic soda is an inconvenient material to weigh out in small quantities, so that it will be better to make up a stock of 10% solution. The rest of the materials can be made up into a solution double the strength in the formula, thus : — A. Hydroquinone, . 16 grams, . 160 grains. Sodium sulphite, . 70 ,, . IJ ozs. Citric acid, . . 1 „ . 20 grains. Potassium bromide, 4 ,, .40 „ Water up to 1000 c.c., . 20 ozs. EIKONOGEN. 67 B. Caustic soda 10°/o solution, 80 c.c., If ozs. or Sodium carbonate 107o ” Water up to . . . 1000 „ 20 „ For use take equal parts A and B. The same quantity of water may be added with advantage if the plate is not under-exposed. The strong alkali used in this developer is liable to cause frilling. Eikonogen is a complicated organic sodium salt (see index). It is not a convenient developer to use, as it dissolves in water with difficulty and deteriorates rapidly when it has dissolved. Its action is very powerful, however, and many workers use it for developing snap-shots, lantern slides, and badly under-exposed plates. The follow- ing formula is recommended : — A. Eikonogen, . . .5 grams, 24 grains. Sodium sulphite, . . 20 „ 96 „ Water up to . . 300 c.c., 3 ozs. B. Sodium carbonate (crystals), 15 grams, 70 grains. Water up to . . 100 c.c., 1 oz. For use take 3 of A to 1 of B immediately before developing. It is not advisable to make up more than is required for immediate use. Bromide, if used at all, must be introduced very sparingly. For very under-exposed plates, the following may be used instead of B : — Caustic soda 10°/^, ... 50 c.c., | oz. Water up to . . . . 100 ,, 1 „ 68 METOL. MetoP possesses a marked effect in bringing out detail in under-exposed plates, and a mixture of this with hydroquinone is perhaps even more effectual. It is an excellent developer, being preferred by many people to pyrogallic acid. The following is a good formula : — Metol, . . . . *8 grams, Sodium sulphite (crystals), . 5’5 „ Sodium carbonate (crystals), 4*5 „ Potassium bromide, . . *2 ,, Water up to . , 100 c.c., 4 grains. 24 20 1 1 5 > J) oz. It is well to dissolve the metol first and then add the other constituents. Some people are very sensitive to the action of metol, which sets up violent inflammation in their hands. Amidol is, chemically speaking, di-amido-phenol or pyrogallic acid in which two of the OH’s are replaced by NHg. This last is derived from ammonia, NHg, in the same way that OH is derived from water, OHg, and plays a very important part in organic chemistry. - Pyrogallic acid. CaH 3 OH OH OH Di-amido-pbenol (amidol). C0H3 NH2 NH^ OH It is a powerful reducing agent, and has the For chemical formula see index. AMIDOL. 69 peculiarity of working without an alkali. The image comes up very quickly when using amidol, and care must be taken to leave the plate in the developer until it has attained sufficient density. Amidol dissolves more readily in a solution of sul- phite than in water, and sulphite has an accelerating action with this developer. Amidol keeps very badly, and it is advisable to make up fresh solution for each batch of plates. It is not easy to restrain this developer, as bromides do not seem very effectual with it. The presence of a small quantity of bromide, however, (say 1 drop of a 10°/o solution to each ounce of developer) prevents any tendency to fog. Amidol, . . . . ’5 grams, . 2 ^ grains. Sodium sulphite (crystals), 3*0 „ .15 „ Water up to . . . 100 c.c., . 1 oz. In case of under-exposure, add 1 c.c. to each 100 c.c., or 5 or six drops to each oz. of a 10°/o solution of sodium carbonate crystals, and the same quantity of potassium bromide. Paramido-phenol is hydroquinone in which one OH has been replaced by NHg. Hydroquinone. p TT / OH I OH Paramido-phenol. OH NR, Its hydrochloride, or compound with hydrochloric acid (C 6 H 4 .OH.NH 2 .HCl), is usually employed and is sold in solution as “ Eodinal,” which keeps 70 EODINAL, GLYCIN. excellently. Those who use it speak very highly of it as an all round developer, and the author has obtained good results with it in radiography. It is convenient to make up a strong solution, similar to rodinal, and dilute it when required. Strong solution — Paramido-phenol hydrochloride, *5 grams, 25 grains. Sodium sulphite, . . .9 „ 1 oz. Sodium carbonate (crystals), .9 „ 1 „ Water up to . . . 100 c.c., . 10 ozs. For use, take — Strong solution (Rodinal), . . 10 c.c., 1 oz. Potassium bromide 10°/o solution, . 2 „ J „ Water up to . . . . 100 „ 10 „ Glycin* gives hard, sharp negatives, and acts slowly. It is useful, therefore, in copying line drawings and similar subjects, and works well with kinematograph films. Glycin is rather insoluble by itself, but dissolves readily in alkali and sulphite. The following is a good formula : — Glycin, .... *8 grams, . 4 grains. For convenience, it may be made up four times this strength and diluted for use. o Sodium sulphite (crystals), 2 Sodium carbonate (crystals) Water up to I . 10 . 15 1 oz. * For chemical formula see index. HYDROXYLAMINE. 71 Hydrazine (N2H4) and hydroxylamine (NH2.OH) have been proposed as developers, the latter by Spiller and Egli. They are only of scientific in- terest, however. As regards the majority of these developers, it is difficult to say that one is better or worse than another. The best (feveloper is undoubtedly the developer that suits the photographer’s particular method of exposing, developing, and printing. The same dictum applies to the various formulse, which must not be taken as absolute, but merely as general guides, to be varied according to circum- stances. Before closing the subject of development, atten- tion must be paid for a few moments to the work of Hurter and Driffield, whose results are quite easy to understand. In a perfect negative, containing only black and white and no yellow stain, you have minute black spots on a transparent ground. Supposing you had a small plate, say one inch each way, and you divided it by cross lines into ten thousand equal squares and then stopped up nine thousand, so that no light could come through these particular squares, you would have something that would represent roughly a photographic negative. If you put this in a printing frame against the light, only one-tenth of the light falling on the plate would come through. Supposing another similar plate were placed behind the first plate, it would pass one -tenth of the light that had filtered through the first plate, one- 72 HURTEK AND DRIFFIELD tenth of one-tenth of the original light. The light coming through a third similar plate would he one- tenth of one-tenth of one- tenth of the original, and so on. That is to say, the light coming through each of the three plates would be -^th, etc., of the original, or taking it the reverse way, the ratios between the lights w^ld be 10, 100, 1000, etc. Now the logarithms of 10, 100, 1000, etc., are 1, 2, 3, and so on ; so that the logarithm of the light stopped by one screen or one density is 1, by two screens, 2, by three screens, 3, etc. Supposing you want to photograph a scale of tones so graded that they are in the order 1, 2, 3, 4. A correct result will only be obtained if the printing values of the different parts of the negative are 1, 2, 3, 4 ; that is to say, “ each density must be proportional to the logarithm of the light intensity that produced it.” By experiment Hurter and Driffield found that for every plate there was a particular exposure, within the limits of which this law held good ; above and below these limits the ratios were false. More than this, they found that the gradation in a negative, developed with ferrous oxalate, could not be altered by any amount of development, supposing no fog was introduced, but depended entirely on the exposure. On this was based the H and D system of deter- mining the sensitiveness of plates. The plate receives exposures from a standard light graduated from 2 ^, 5, 10, 20, 40 to 160 secs., the first portion of it, called the “ fog strip,” receiving no ex- SPEED MEASUREMENT. 73 posure at all. This plate is developed in the standard developer for a standard time at a standard tempera- ture (see p. 54), and the densities of the different strips are read on a photometer, and recorded in the manner shown below (fig. 6). The bottom line of Fig. 6. — Speed readings of two plates — A, ordinary ; B, rapid. the chart represents the logarithms of the exposures, and the upright line the densities read on the photo- meter, the density of the fog strip being subtracted from each one. It will be noticed that several of the dots are in a straight line ; this is the period of correct exposure. The straight line is prolonged to meet the base line, and the number read off, which gives the “ inertia ” of the plate, or the exposure 74 INFLUENCE OF PYRO-STAIN. correctly. To obtain the H and D speed number, the figure where the straight line cuts the base is read off, and this divided into 34 gives the speed number required. ' The important points brought out by Hurter and Driffield, in addition to the accurate method of determining the speed of plates, are first, that the gradation in a negative cannot be altered during development, unless fog or stain is introduced ; and secondly, that pyro-ammonia is a very uncertain de- veloper. Another point arises out of the former one, namely, that sensitiveness of the plate is as much a matter of the developer used as of the state of the emulsion itself, the speed number of the plate developed with pyro-soda being much higher than when developed with ferrous oxalate, and the speed number with metol, for instance, is higher still. The Hurter and Driffield system, as has been pointed out, takes no account of the yellow stain produced by development with pyrogallic acid and other, organic developers. Alfred Watkins and others have given considerable attention to this matter, and have shown that the “ pyro stain ” has an important influence on the printing value of the negative. This pyro-stain is something more than a mere stain, for if the silver be dissolved out of the plate with nitric acid, a faint yellow image remains. Light, oxidising agents, tannin, and other agents cause gelatin to become insoluble. This is probably the explanation of the pyro-image. Various agents TANNING OF GELATIN. 75 first action of the cyanide is to form insoluble silver are present, such as the oxidized pyrogallic acid which resembles tannin in some respects, and the nascent compounds set free when the silver bromide is reduced, whilst the action of the light itself on the gelatin, and other little known causes, are at work to “ tan ” the gelatin. Wherever the gelatin becomes insoluble, — and this is most likely to happen where the chemical action of building up the silver image is taking place, — it fixes some of the highly coloured products of the oxidation of the pyrogallic acid or other phenolic developer. As regards the “ tanning ” of the gelatin or rendering it insoluble, formaldehyde (see p. 76) has a strong action and is used to prevent plates frilling in hot weather. Plates washed with formaldehyde may be dried by means of heat, that could not be applied in the ordinary way without melting the gelatin. Formaldehyde is supplied commercially in 40 per cent, solution. This should be diluted as follows, and the plate should be immersed for ten minutes, being well washed afterwards : — Formaldehyde (40°/^ solution), . . 1 part. Water, . . . . . .3 parts. Following up the work of Schwartz and Mercklin, and of Hellheim, Messrs. Lumiere and Seyewitz have found that formaldehyde is not the only alde- hyde capable of tanning gelatin. Aldehydes add to the reducing power of the developer, but only in 76 FORMALDEHYDE, ACETONE. required before the plate commences to register effect to aldehydes, and can be used advantageously to take the place of the alkali. With pyrogallic acid, development is effected rapidly; with hydro- quinone, the development is not so rapid, but the results are as vigorous as with alkaline carbonates. Lumiere and Seyewitz find that the addition of formaldehyde (formalin) to the developer causes strong staining of the film, with the exception of paramido-phenol (rodinal) and metol developers. The following are the formulae proposed for development with acetone and sulphite in place of an alkali : — A. Pyrogallic acid, . . 1 ’8 grams, 9 grains. Water, . . . 100 c.c., 1 oz. Sulphite of soda (crystals), 1 1 grams, 56 grains. Acetone, . . . 2 ’5 c.c., 12 minims. B. Hydroquinone, Sulphite of soda, Acetone, Water, . . 3 . 20 . 10 100 grams, 15 grains. „ 100 „ C.C., 50 minims. jj 1 oz. When the plate has been developed to the right density, it is washed carefully under the tap, and allowed to soak for a few minutes in water ; then it is fixed, i.e., the unaltered silver salts are dissolved out of the film, so as to leave no material sensitive to light on the plate. The principal, and practically the only, substances used for this purpose are potassium cyanide and sodium thiosulphate (“ hypo ”). The action of the two solvents is very similar : the FIXING. 77 cyanide by double decomposition with the silver bromide, and then to make a double silver potassium cyanide, which is soluble in water. Potassium Silver Silver Potassium cyanide. bromide. cyanide. bromide. (1) KCN + AgBr = AgCN + KBr. (2) KCN + AgCN = KCN,AgCN. With thiosulphate, silver thiosulphate is first formed, and then a double soluble thiosulphate of silver and sodium. Sodium Silver Silver Sodium thiosulphate. bromide. thiosulphate. bromide. (1) ^28203 + 2AgBr = Ag 2 S 203 + 2NaBr. (2) Ag2S203 + Na2S203 = Ag2S203 , Na2S203. The quantity of potassium cyanide to be used will be found under the development of wet plates (p. 41, which see). Of sodium thiosulphate, solutions vary- ing from 40 to 10 of the crystals in 100 of water can be used, the former for negatives and the latter for prints. Haddon and Grundy have shown that 10 per cent, is the best strength for fixing prints on albumenized paper. It is well to employ a saturated solution of the salt (50 per cent.), and dilute just before starting development. Acids decompose sodium thiosulphate into sul- phurous anhydride (sulphurous acid gas, or burnt sulphur) and free sulphur. The reader should try the experiment of adding a little hydrochloric acid to a little solution of sodium thiosulphate. In a few moments he will be able to smell the burnt 78 ACID THIOSULPHATE. the presence of sulphite. Acetone has a similar sulphur, and will see the liquid turn milky with free sulphur, thus — + 2HC1 = 2NaCl + H 2 O + Sulphurous acid has a very strong bleaching action and the sulphur is liable to cause stains. Acid or alum, which contains free acid, should never be added to the fixing bath. As soon as the fixing bath begins to work slowly it should be thrown out and a fresh lot made up. Exposure to the air gradually oxidizes the thio- sulphate and sets up decomposition. Old baths full of dirt and pyro-stains should not be used, as they are almost certain to bleach or discolour the negative or print. As regards the washing of negatives free from thiosulphate after fixing, the reader is referred to page 14. Sodium Hydrochloric Sodium thiosulphate. Acid. chloride. Water. Sulphurous anhydride. so. Sulphur. + s. POSITIVE AND NEGATIVE. 79 CHAPTEK V. Keveksal. In one sense it is largely accidental that a “ negative ” is produced by the ordinary method of exposure and development. If a piece of paper be coated with ferric oxalate and exposed in the camera, the reduced image will be lighter than the unreduced, that is to say, a positive will be produced. If this be washed over with ferricyanide of potassium, the positive will be converted into a negative ; if ferrocyanide had been used, the positive would have remained positive. All chemical reactions are reversible, given proper conditions. In a mixture of substances such as exists in the film of a sensitive plate, where there is no outlet for the products of decomposition — the excess of bromime or other halogen set free on reduction in this case — a state of equilibrium is reached at a certain point. If decomposition is carried beyond this point, reversal sets in, which may go the whole way until the original compounds are re-formed. 80 REVERSAL. This occurs in actual practice in photography. When a plate is over-exposed the high lights are thin after development, i.e., partial reversal has taken place. By great over-exposure reversal can be carried to such an extent that a positive is obtained instead of a negative. This process is actually employed for copying negatives without going to the trouble of making a transparency and printing from that again. The resulting negative is reversed as regards right and left, which is a draw- back if needed for ordinary photographic printing, though it is an advantage in many “ process ” applica- tions. The actual method of accomplishing this, due to T. Bolas, is as follows : — Soak a gelatino-bromide dry plate for five minutes in a 4 per cent, solution of bichromate of potassium, rinse once or twice, and then dip into a bath of equal parts of methylated spirit and water. Blot off the superfluous moisture and allow the plate to dry, all these operations being conducted in the dark room. Then expose the plate in a printing frame behind the original negative, and expose to direct sunlight for three or four minutes. On removal from the frame in the dark room a faint image will be seen on the plate, which is developed and fixed as usual. A chloride plate must not be used for this purpose, as the re- duction of silver chloride cannot be reversed in the same way as silver bromide. Several chemicals have the power of reversing a HALATION. 81 plate in a similar manner to light. Sodium hypo- phosphite has this peculiarity. The organic substance thiosinamine and the organic salts known as thiocar- bamides when added to the developer have this effect. Colonel J. Waterhouse recommends for this purpose the following developer : — A. Lithium carbonate saturated solution, . . 100 C.C., . 1 oz. Eikonogen, . . 1 gram, . 5 grains. Sodium sulphite, . 1 „ -5 ,, Dissolve the two latter in the first just before using, and add a few drops of B. Ammonium bromide, . . .1 part. Thiocarbamide, . . . .3 parts. Dissolved in water (quantity not stated). “ Solarization ” is the word usually employed to denote the local reversals that sometimes occur on plates containing very strong contrasts. “ Halation ” or the veiling or blurring of the edges of the high lights, such as the sky-lines of houses or the branches of trees taken against the light, is a species of partial reversal, generally attributed to reflection from the back of the plate. To prevent this it is usual to “ back ” the plate with some non-actinic medium, such as caramel and burnt sienna. The following formula, due to J. S. Teape, is a good one : — Boil 1 lb. of white lump sugar in a saucepan large enough to hold twice the bulk, for one hour after it has F 82 BACKING PLATES. melted, stirring with a wooden rod the whole time. Allow the liquid to cool slightly, then add, in small quantities at a time, 4 ounces of hoiling water, and stir between each addition. Of this caramel take . . • Saturated solution of gum tragacanth, 1 oz. Powdered burnt sienna, . . 2 ozs. Methylated spirit, . . . 2 ,, Add the spirit after the other ingredients are well mixed. Apply thinly to back of plate by dabbing with flat hog’s-hair brush. Instead of making the caramel from the sugar, it can be purchased ; the dry powdered form is the best. Some recent work of the author’s seems to show that the caramel alone is sufficient to stop halation, and that the following formula is satisfactory : — White starch or flour. Caramel powder. Sodium carbonate (crystals). Methylated spirit. Water, . . . . 10 parts. 10 2 25 75 }> jj >5 }J Boil the water first ; mix the starch into a thin paste with part of the water (cold) and pour into the boiling water ; then add the caramel and, when thoroughly incorporated and cold, the spirit. FEREICYANIDE REDUCTION. 83 CHAPTEK VI. Eeduction, Intensification, etc. If the image in the negative is too dense, it is sometimes necessary to reduce its intensity. Any per-chloride, such as per-chloride of iron, or similar salt, will have the effect of converting the silver of the image into chloride. This must be associated with an agent, such as thiosulphate of soda, which is capable of dissolving the silver chloride as it is produced, otherwise it would be difficult to know when the reduction had proceeded far enough. The method generally used in practice is that of Howard Farmer, in which a mixture of potassium ferricyanide and sodium thiosulphate is employed. The action is very simple, silver ferricyanide being produced, which dissolves in the thiosulphate. The reducing mixture should be made up in small quantities at a time, as the thiosulphate slowly reduces the ferricyanide, rendering the mixture useless. The negative should be soaked in water 84 INTENSIFICATION. for ten minutes, and then be placed in a 12^ solution of sodium thiosulphate to which a certain quantity of 10% solution of potassium ferricyanide has been added ; the amount can be regulated according to the rapidity of reducing action re- quired. All the hypochlorites act on the silver image and can be used to reduce its density. Intensification is very commonly employed, especially in wet plate negatives. All the methods employed have for their object the conversion of the particles of silver into some compound that will increase the printing value. With the ex- ception of a few cases, the image is first bleached with mercuric chloride, which converts the black silver image into a white double silver-mercurous chloride. This must be washed carefully before proceeding to the next stage, and it is absolutely necessary to success in intensification that the film be thoroughly cleansed from “ hypo.” Mr Chapman Jones has done a great deal of valuable work on intensification.^ He finds that the old method of treating the bleached plate with ferrous oxalate developer is by far the most reliable method. The plate is first of all treated to a bath of dilute hydrochloric acid containing one part in one hundred and is then soaked in Per-chloride of mercury, . . 2 parts. Water, ...... 100 „ * See Royal Photographic Society's Journal, June 1897, and earlier issues. VAEIOUS INTENSIFIERS. 85 until thoroughly bleached. After well washing, the plate is placed in a bath of ordinary ferrous oxalate developer (which see) until quite black, when it is again washed. If not sufficiently intensified the whole operation may be repeated a second, and even a third time, the chemical effect being to form an amalgam of silver and mercury, which, through the pt'otection afforded by the gelatin, is permanent. A very common method is to treat the bleached plate with very dilute ammonia. The action in this case is very complicated, as the black intensi- fied image consists principally of uncertain com- pounds of ammonia and mercury, the silver being largely dissolved out. Consequently, the effect on the plate is by no means uniform, the thinner parts being actually reduced by the solvent action just referred to. If employed, the ammonia solution should contain about ten drops of liquor ammonia •880 to the ounce. Sulphite of soda can be used after bleaching with mercury, but the intensifying action is not very strong or certain. The chemical effect is to reduce part of the silver and mercury to the metallic state, and to dissolve part as sulphites. A mixture of potassium iodide and potassium cyanide is sometimes applied to the bleached plate. It is uncertain in its action, and changes take place on storing, as they do with plates blackened by ammonia. The same applies to a mixture of 86 SILVER AND LEAD INTENSIFIERS. silver nitrate and potassium cyanide sometimes employed. Wet plates are frequently intensified by silver nitrate mixed with an acid developer, such as pyro- gallic acid containing citric acid, the following being employed at the Bolt Court Process School : — A. Silver nitrate. Water distilled, . 22*8 grams, 1000 C.C., B. Pyrogallic acid, . 11*4 grams. Citric acid, . 28'5 „ Water distilled, . 1000 c.c., 200 grains. 20 ozs. 100 grains. 250 „ 20 ozs. Perricyanides of uranium and lead are occasion- ally used, the action being to form an insoluble ferrocyanide. It is therefore very important that in making the solution the crystal of ferricyanide of potassium be washed free from any adhering ferro- cyanide. The uranium ferrocyanide is red in colour, and is very opaque to the rays causing photographic action, so that care must be taken not to over- intensify. The lead ferrocyanide is white, and must be treated with ammonium sulphide, which turns it into black sulphide of lead. Instead of the ferri- cyanides of lead or uranium, a mixture of potassium ferricyanide and lead or uranium nitrate is used. Lead Intensifier. Lead nitrate, . . 4 grams. Potassium ferricyanide, 6 ,, Acetic acid (glacial), 2 c c., Distilled water up to 100 ,, . 20 grains. . 30 „ . 10 minims. . 1 oz. LEAD AND UEANIUM. 87 Uranium Intensijier. Uranium nitrate, . . 1 gram, Potassium ferricyanide, .1 ,, Acetic acid (glacial), . 2 grams. Distilled water up to 100 „ . 5 grains. . 5 . 10 . 1 oz. J5 Mr. Charles W. Gamble has pointed out an interesting point in connection with intensification of half-tone negatives by lead. If the mixture of lead and silver ferrocyanides is treated with fresh ammonium sulphide, the dots in the negative come out sharp and black, but if the ammonium sulphide has been made up several days, each dot is sur- rounded by a grey margin instead of being sharp. The explanation of this is, that on exposure to the air, ammonium sulphide is oxidized to a mixture of thiosulphate and polysulphides which have a solvent action on the silver, which is first dissolved and then re-precipitated as a blurred margin round the dot. 88 PHOTO-SALTS CHAP TEE VTI Feinting in Silver. From the short account given on p. 36, the reader will have learnt something about the photo-chlorides of silver, which Carey Lea did so much to investigate. These intermediate compounds between ordinary silver chloride and metallic silver are of most varied colours, ranging from white through shades of red and purple to black. They are permanent in the dark, hut are altered by light. Besides these coloured photo-chlorides and other photo-salts of silver there are several coloured varieties of metallic silver, which in this state more resembles a colloid substance (see p. 113), and possesses the remarkable property of dissolving in water. In addition to the ordinary white form of metallic silver, there seem to be at least four other modifications. The first, which we may call A, is soluble, forming a deep red solution in water. When concentrated, or if nitrate of ammonium is added to the solution, it forms a precipitate, which may be either matt black, blue or green, whilst moist. As soon as it is dry, however, SOLUBLE SILVEK. 89 it acquires a brilliant metallic surface, having a bluish-green tint. Modification B is insoluble, and is produced from the foregoing ; it is dark reddish- brown when moist, but resembles A when dry. The third form, C, is of a dark bronze hue when moist, but like burnished gold when dry. No soluble modification of this exists, but a copper- coloured variety is formed under certain conditions. All the varieties have the remarkable property of drying with their particles in optical contact, pro- ducing perfect mirrors if spread out on paper and allowed to dry. Unfortunately, like the photo- chlorides, these forms of metallic silver are affected by light ; A and B become brown after some hours, and the coppery modification of C becomes bright yellow. In spite of this, several occasions can be imagined on which they would be serviceable for making a large mirror for immediate use in the studio, or where a large reflecting surface is required. C has the property of changing into ordinary silver of great beauty in presence of moisture, and immedi- ately on being subjected to friction in any part, the action spreading to the rest of the film. The reader has probably seen a good many of these photo- chlorides and varieties of metallic silver in the ordinary silver printing papers after exposure behind the negative. The old process of sensitizing albumen paper with silver nitrate is still the most largely used of any printing process in spite of numerous drawbacks. 90 ALBUMENIZED PAPER. In preparing the paper on a large scale, the eggs are broken separately, the whites separated from the yolks and run into drums. This albumen is then run into churns driven by steam, and “ frothed,” being allowed to stand until quite limpid, when it is decanted off from the embryos and stringy portions of the white of egg and run into tall glass jars to ferment. After this it is filtered and again treated to the frothing process and allowed to settle, the stringy portions being now finally removed. Ammonium chloride is added to the albumen, and Eives or Saxe paper is coated by fioating the sheets on the surface of the liquid. The paper is hung up to drain, stored for some time and re-albumenized, being hung up to drain the reverse way. This pro- cedure equalizes the quantity of albumen on the surface. From this description of work on the large scale, the reader will see how to proceed in the small way if ever he finds it necessary to do so, the* following quantities of materials being used, and a whisk being employed instead of a churn: — Albumen, . Ammonium chloride, Eectified spirit, . Distilled water, . 6 ozs. . 60 grams. . 96 minims. If ozs. The paper is sensitized just before use by fioating on a solution of silver nitrate containing 50 grs. to the oz., or 10 grams in 100 c.c. PRINTING AND WASHING. 91 The action of the sensitizing bath is to convert the silver nitrate into chloride, which is entangled in the albumen by interaction with the ammonium chloride. Besides this, however, the silver nitrate has an important action on the albumen, forming an albumenate of silver, which is insoluble in water, so that the albumen does not dissolve off the paper. Consequently, the stronger the sensi- tizing bath the longer will the paper have to be floated, as the silver nitrate penetrates more slowly through the insoluble albumenate. In printing on this paper the action is probably very complicated as the albumenate of silver takes part in the reduction as well as the chloride. The ready sensitized paper, used so largely by amateurs, contains citric acid in addition to the other con- stituents, which still further complicates matters. When printed, the paper is washed in water con- taining one part of common salt in 40, and toned with gold or other more or less permanent reducible metal, in order to counteract the objectionable red tones of the silver print. In washing the print before toning, the reason that the water turns milky is that the soluble silver salts react with the salt in the water to form chloride. Of the numerous toning baths, the acetate is that most usually employed. The gold chloride generally purchased is a double chloride of gold and sodium and is frequently acid. It is important, therefore, to neutralize the gold chloride solution by shaking 92 TONING WITH GOLD. it up with a little powdered chalk. For use it is convenient to dissolve the contents of the 15 grain tube in IJ ounces of water, making approximately 1 grain to 1 dram or a 2 per cent, solution ; or if dissolved in 50 c.c. of water, a practically 2 per cent, solution of the commercial salt, or a 1 per cent, solution of gold is obtained. The following Table shows a few of the various formulae recommended by different workers for toning sensitized paper with gold. TABLE VIII.— Gold Toning Baths. Each to be made up to 10 ounces with water. Substances. I. II. III. IV. V. VI. VII. Gold chloride (commer- 2 2 2 2 1 1 2 cial), 2% solution, . drams drams drams drams dram dram drams Acetate of soda, . 90 grains 48 grains Borax, .... 96 grains Bicarbonate of soda, 4 grains 30 grains Carbonate ,, (washing soda), 10 grains — Phosphate of soda. 20 grains Tungstate of soda, — 40 grains When toning has reached a stage where the blue of the gold neutralizes the objectionable red and orange tones of the original, the print is fixed in a 10 per cent. (2 oz. to the pint) solution of sodium thiosulphate. It is even more important with prints than with negatives to always keep the fixing bath in perfect condition. The least trace of acid CHEMISTRY OF TONING. 93 means the presence of free sulphur (see p. 77 ), and free sulphur turns the whites of the print yellow. For this reason combined toning and fixing baths cannot be too strongly condemned. Consequently, the fixing bath should be made alkaline by the addition of ammonia, or, better, bicarbonate of soda in the proportion of 5 grains to each ounce of “ hypo.” Always test with litmus paper before use ; if acid, i.e., if the litmus paper turns red, add more bicarbonate. Toning baths should be made alkaline with bicarbonate in the same way, if on the acid side, as it is essential that the bath be alkaline. After toning it is well to immerse the prints in salt and water before fixing. They may be left here until all the batch has been toned, so as to avoid contamination of the fingers with the fixing bath whilst toning is in progress. The chemistry of the toning process is as follows : In the alkaline solution the gold chloride is reduced first of all from auric chloride (Au CI 3 ) to aurous chloride (Au Cl) ; then an atom of gold is deposited, an atom of silver taking its place, thus, Aurous chloride. Silver. Silver chloride. Gold. AuCl 4- Ag = AgCl + Au. From this it is clear that other metals can be used for toning instead of gold. With a platinum toning bath, for instance, platinum is deposited in the place of the silver, and with a lead toning bath, lead is exchanged for the silver in the print. The 94 GELATINO-CHLORIDE PAPER. following platinum toning bath is recommended by Liesegang : — Potassium chloroplatinite, . *1 gram, | grain. Nitric acid, . . . ”5 c.c., . 2 minims. Water, .... 100 „ . 1 oz. Gelatino-chloride and collodio-chloride papers are emulsions of silver chloride and an organic salt with gelatin in the one case and with collodion in the other. These papers are generally known as printing-out ” papers. W. K. Burton’s formula for gelatino-chloride emulsions is as follows : — A. Ammonium chloride. Gelatin, . Distilled Water, Soak the gelatin and water for an hour and then add Silver nitrate, . Distilled water, B. Sodium citrate. Gelatin, . Distilled water. Allow to soak for an water-bath ; then add Silver nitrate, . Citric acid, Distilled water. 3*5 grams, . 53 grains. 27 „ . 420 „ 850 C.C., . 30 ozs. ammonium chloride in the dissolve on a water-bath ; 9*7 grams, . 150 grains. 14 C.C., . J oz. 2 grams, . 30 grains. 6*3 „ . 100 100 C.C., . 3J ozs. hour and dissolve in the 3 grams, . 45 grains. 5 „ .80 14 C.C., . J oz. COLLODIO-CHLORIDE PAPER. 95 Mix A and B ; wash as directed in dry-plate emulsions, and after keeping for three or four days, coat the paper by floating. Geldmacher’s formula for collodio-chloride emul- sion is as follows : — A. Pyroxylin, . 22*75 grams. 6J drams. Ether (not methylated), 425 C.C., 15 ozs. Alcohol (not methylated), 425 „ 15 „ Castor oil, . 3-5 „ . 1 dram. B. Silver nitrate. 20 grams. 308 grains. Distilled water, . 21*5 c.c., 6 drams. Alcohol (not methylated), 42*5 „ IJ ozs. C. Citric acid, . 5 grams, 7 5 grains. Alcohol, 70 C.C., 2J ozs. D. Strontium chloride, 5 grams. 7 5 grains. Alcohol, 70 C.C., 2 J ozs. Mix C and D and add to A, shaking vigorously. In the dark room, add B to the mixture in small portions at a time, shaking constantly. The emul- sion is ready for use after standing for an hour. Alpha paper is essentially a gelatin emulsion of silver citrate. The following is Wellington’s formula : — A. Silver nitrate, . Citric acid. Distilled water, . 53*5 grams, 53-5 „ 142 C.C., 825 grains. 825 5 ozs. B. Sodium chloride, 10 '7 grams. Potassium bromide, 21*4 ,, Citric acid, . 53*5 „ Gelatin, . . 21*4 „ Distilled water, 142 c.c.. 165 grains. 330 825 330 5 3 ) 33 OZS. 96 TONING PKINTING-OUT PAPERS. Both solutions are to be heated to 66° C. A is then added to B, and 1600 grains (10 4 grms.) of gelatin, previously swollen and melted, is added to the mixture, which is run into a dish and allowed to set. It is then broken up, washed and re-melted before coating the paper, which is best developed with the hydroquinone formula given below (p. 95) and toned. As regards toning, the collodio- and gelatino- chloride papers may be treated alike. The same baths may be used as for ordinary sensitized paper, but these papers work better in a bath composed of ammonium sulphocyanide and gold chloride than in any other. The quantity of sulphocyanide may vary considerably, but as it has a tendency to dis- solve gelatin, it is not advisable to use more than is recommended in the formula. These printing- out papers require to be toned somewhat more deeply than ordinary sensitized paper. The gelatin paper should not be touched with the fingers as the gelatin is apt to soften with the warmth, and retain the marks ; for the same reason, all solutions should be kept cold. To prevent uneven toning, it is well to give the prints a thorough washing, preferably in salt and water (see p. 87), before toning. The following bath can be recommended : — Gold chloride (2% solution), . 6 c.c., 1 dram. Ammonium sulphocyanide (10% solution), . . . . 30 ,, 5 drams. Water, ..... 100 ,, 16 ozs. TONING AND FIXING BATHS. 97 Ammonium sulphocyanide is very deliquescent, and should be dissolved in water at once to form a 10% solution. In making up the bath, always mix the sulphocyanide with the water first, and then add the solution of gold chloride. In toning, it should always be borne in mind that the number of prints that can be toned with a given quantity of gold depends quite as much upon the nature of the prints as upon their size. A dark print with heavy shadows may require three or four times as much gold as a light print of, say, a cloud effect. It is important when economy of gold is desired, to trim the prints before toning. The following formula has been strongly recom- mended by printers : — Gold chloride (2% solution), 1*5 c.c., . 3 drams.__ Ammonium sulphocyanide (10% solution), . . 20 ,, .2 ozs. Sodium thiosulphate, . 1 gram, . 5 grains. Water up to . . . 100 c.c., . 10 ozs. Numerous other formula3 are in existence and will be found in the various year books and other books of reference, but exigencies of space forbid their inclusion here. Some photographers use and recommend the combined toning and fixing baths. These may be all very well for routine work in careful and experienced hands, but they are wrong in principle and the least carelessness may produce disaster. The author never uses them himself, and gives the G 98 PRINTlNG-OUT PAPERS. following formulae, which is due to Dr Liesegang, under protest, so to speak : — Ammonium sulphocyanide (10% solution), . . 10 C.C., 10 drams. Distilled water up to . 100 c.c., 12 „ To 60 parts of this solution, add 7 parts of a 2^ solution of gold chloride, diluted with an equal bulk of water. When the mixture has been made, add 40 parts of old, used, combined bath. Printing-out papers can be developed after a short exposure, and can then be toned and fixed in the usual way. Only a faint image is required to start with, and it is advisable not to print beyond the point where the details just begin to show in the half-tones. It is well to follow the excellent sug- gestion of Mr Wilson of the Paget Prize Plate Co. and immerse the prints in a 10% solution of potas- sium bromide before developing, thus changing the silver chloride into silver bromide. After soaking in this solution for from 10 to 20 minutes, passing a clean camel-hair brush over the surface of the paper to ensure the absence of bubbles, the paper should be thoroughly washed for about ten minutes in run- ning water to remove excess of potassium bromide, which would render the development too slow. Then develop with the following: — Common salt, . Alum, .... Sodium thiosulphate (hypo). 4 grams, 240 grains. 2 „ 120 „ 15 „ 2 ozs. BROMIDE PAPER. 99 A. Hydroquinone, . 2 grams, . 10 grains. Sodium sulphite, . 2 „ .10 „ Sulphurous acid, . 1 c.c., . 5 minims. Water up to . . 100 „ . 1 oz. B. Sodium carbonate (washing soda), . 5 grams, . oz. Water up to . . lUO c.c., . 10 ozs. For use, take one part each of A and B, and one part of water. The papers can be toned with platinum ; for formula see p. 94. Bromide paper is coated with a gelatino-broniide of silver emulsion similar to that used for dry plates, but generally much less rapid. The follow- ing is Dr. Eder’s formula for an emulsion suitable for coating paper : — A. Ammonium bromide, . . 20 parts. Gelatin, .... 50-80 „ Distilled water, . . . 400 „ Soak the gelatin in the water for 12 hours, then dissolve in the water-bath at 50-60° C., and add the bromide. Take the emulsion into the dark room and add, with constant shaking, Silver nitrate, . . . .30 parts. Distilled water, .... 400 ,, After standing for about an hour, pour out into a dish to set, squeeze through muslin, and wash in the manner described on page 52. The above formula gives black tones. If brown tones are required, 100 BROMIDE PAPER. replace two parts of the ammonium bromide by two parts of potassium iodide. Bromide paper may be developed with ferrous oxalate or with most of the dry plate developers, except pyrogallic acid. The author much prefers ferrous oxalate. The following is a good formula : — A. Neutral oxalate of potash, 23 grams, 1 lb. avoir. Distilled or boiled water, 100 c.c., 3J pints. B. Ferrous sulphate, . .30 grams, 1 lb. avoir. Sulphuric acid, . . *5 c.c., 15 minims. Distilled or boiled water, 100 „ 54 ozs. For use, add one part of B to six parts of A, not the reverse, or a precipitate of ferrous oxalate would be formed. A few drops of 10% potassium bromide solution may be added as a restrainer. If after development the prints were to be put direct into water, a precipitate would be formed in the paper of ferric hydrate. To avoid this, the paper is placed in dilute sulphuric acid (say oz. in a pint, or 25 c.c. in 1000 c.c.), which dissolves out any iron from the paper. As regards development with agents other than ferrous oxalate, the combinations that can be made are almost unlimited. For practical purposes, any of the formulae used for dry plate development may be employed, but the strength must be only one- third of that given in the formulae for dry plates. The proportion of sulphite in each ounce or 100 c.c. of developer, however, may remain the same or be TONING BROMIDE PRINTS. 101 only slightly reduced, so as to ensure absence of stain. Bromide prints are frequently toned with platinum or uranium salts. In the former case, the platinum replaces the silver to a greater or less extent. Uranium, although it changes the tone to a reddish- brown, acts principally as an intensifier, and can be applied beneficially to weak prints. It is important that every trace of “ hypo ” be removed by thorough soaking, otherwise toning will be uneven. Selle’s formula for uranium toning is essentially as follows : Uranium nitrate, . . '5 gram, grains. Potassium ferricyanide, . *5 „ ,, Acetic acid (glacial), . dO grams, | dram. Water up to . . 100 c.c., 1 oz. After toning, the print should be washed in dilute acetic acid (say 1 to 30), for twenty minutes or longer. 102 BLUE PRINTS. CHAPTEE VIII. Printing in Salts of Iron. PRACTICALLY the whole of the processes for printing in salts of iron depend upon the fact that ferric salts are reduced to the ferrous state by the action of light, ferric oxalate, Fe% (C^2^4)3> becoming ferrous oxalate, Ee"C204. Potassium ferricyanide converts the reduced salt into insoluble Prussian blue, the unreduced ferric salt being nearly colourless and soluble. If /errocyanide of potassium be used as a developer instead of /errmyanide, the reduced portions remain colourless, whilst the unreduced parts are turned blue. The paper usually employed for reproducing engineering plans and for making blue prints from negatives, is coated with a mixture of ammonio- ferrous citrate, better known as ammonio-citrate or citrate of iron, potassium ferricyanide and gum arabic in water. The process was first employed by PRINTING IN IRON SALTS. 103 Sir John Herschell in 1842. The following is Eock wood’s formula : — A. Potassium ferricyanide, . 10 grams, . 1 oz. Water, .... 100 c.c., . 10 ozs B. Ammonio-citrate of iron, . 30 grams, . 3 ozs. Gum arabic, . . . 5 ,, . J oz. Water, .... 100 c.c., . 10 ozs. Equal parts of A and B to be taken, and after standing for a few minutes until quite clear, the paper should be coated by means of a stiff brush. The paper should be dried quickly and kept dry. It is fixed by washing in water until the whites are quite clear. If over-printed, a little carbonate of soda may be added to the water. If under-printed, fuller density may be obtained by adding a little ferric salt to the first wash water and allowing it to remain until sufficient depth is obtained. This is the same principle as re-developing a gelatino- bromide plate. Spots can be bleached by a weak solution of potassium oxalate. This paper can be toned with various substances. Strong tea containing a little sodium carbonate changes the blue to black, the iron forming an ink with the tannin. The colour can be altered by different reagents, sulphocyanide turning it red, and so on. If the paper be coated with the iron solution (B) only, without the ferricyanide, it can be developed with this solution, or with gold chloride. The process of making a paper for subsequent 104 DEVELOPING BLUE PRINTS. development with ferrocyanide of potassium, whereby the whites of the negative come out white, is as follows, using Pizzighelli’s formula : — A. Gum arabic, . . .20 grams, . 2 ozs. Water, .... 100 c.c., . 10 „ B. Ammonio-citrate of iron, . 50 grams, . 5 ,, Water, .... 100 c.c., . 10 „ C. Ferric chloride, . . 50 grams, . 5 ,, Water, .... 100 c.c., . 10 „ For use, add 20 parts of A to 8 parts of B, and the whole to 5 parts of C. Allow to stand until clear and then coat the paper. As the reduced ferrous is lighter than the ferric salt, the image appears lighter than the back-ground. Develop with : — Potassium ferrocyanide, . 20 grams, . 2 ozs. Water, .... 100 „ . 10 „ Paste the developer on the surface of the print with a brush ; as soon as dark enough, wash, and fix in a 10% solution of hydrochloric acid until the whites show clear. PLATINUM PRINTING. 105 CHAPTEE IX. Printing in Platinum. Platinum printing is not a direct process ; it is really an iron printing process, but instead of bring- ing out the reduced ferrous image with ferricyanide, a platinum salt is used, the platinum being reduced by the ferrous image to form a permanent print. The platinum salt can be incorporated in the sensi- tizing solution that is applied to the paper, as in the cold process, or the iron image can be obtained first by printing on paper coated by ferrous oxalate and treating this afterwards with a solution containing platinum as in the hot -bath process. Platinic chloride PtCl4 can be used, but the effect is not good, as the salt has to be reduced such a long way, so the lower or platinous chloride gives better results. This salt is nearly insoluble in water, but a double chloride of platinum and potassium is very soluble, so that the latter or potassium chloroplatinite, as it is generally called, is the actual salt employed. By the addition of mercuric or palladium salts 106 PREPARING THE PAPER. to the sensitizing solution, “ sepia-” toned images can be secured. The sepia tone does not appear to be due to any admixture of a mercury or pallad- ium compound, but, as V. Hubl has shown, to a peculiar condition of the platinum itself. W. Willis and Captain Pizzighelli are the two best known workers on platinum printing, the hot- bath process of the former inventor being still the most reliable printing method, and that most generally used. Eives paper, No. 74, is sized with arrowroot and gelatin, in some such proportion as the following :* — Arrowroot, . Nelson’s gelatin, . Alum, Water up to 500 grains. 180 „ no „ 120 ozs. The gelatin is allowed to swell and then dissolved at about 80° P. ; the arrowroot, being made into a thin cream with a little of the cold water, is then poured in. The paper is sized on this for about three minutes by floating, and after being hung up to dry is sensitized by coating with a solution made of iron sensitizing salts, supplied in two solutions, A and B, by the Platinotype Co., and chloroplatinite of potassium, as follows : — Iron solution A, . . . .3 parts. Of the mixture take 7 drams, make up to 1 oz. * “E. A.R.” in The Photogram. DEVELOPING PLATINUM PRINTS. 107 with distilled water, and dissolve in it 48 grains chloroplatinite of potassium. Coat the paper in a room heated to 70° F., the atmosphere being kept moist. The paper should be allowed to get surface dry and should then be dried completely on an iron plate in front of a fire, taking care not to overheat. To keep the paper dry, it should be stored in a tin having a lid at at each end, the bottom lid containing asbestos fibre soaked in strong calcium chloride, and dried bone dry by beating on an iron plate. A perforated zinc grat- ing should cover the calcium chloride and asbestos to prevent any contact with the paper. It is important to keep the paper as dry as possible whilst printing, and for this purpose sheets of india-rubber are placed behind the paper in the printing frames. Printing is allowed to continue until a faint iron image is visible, when it is de- veloped with a solution of oxalate of potash at a temperature not lower than 100° F. The solution of oxalate of potash contains — Potassium oxalate (neutral), , .16 parts. Water, 60 „ Hard negatives or under-exposed prints require a hotter oxalate bath, as it tends to soften and flatten the detail. When developed sufficiently, the prints are fixed without washing in a bath containing — Hydrochloric acid, . . . . 1 part. Water, . . . . . .60 parts. 108 TONING WITH CATECHU. The solution is poured away after a few minutes, and fresh poured on, this being again repeated. The object is to dissolve out every trace of iron and unreduced platinum salt. The paper must be washed to remove the acid. Paper is made for developing in the cold, but this paper gives very brilliant results in the hot bath. By adding mercuric or cupric chloride to the de- veloping solution a sepia-tone is produced. Various substances can be used to tone or intensify platinum prints, but with the exception of catechu, they are not to be recommended. Mr J. Packham has done much to introduce toning with catechu, and M. A. Villain contributed an interesting article last year to The Photogram on the subject. The toning-bath is prepared by boiling 7 grams of powdered Bombay catechu with 150 c.c. of water for ten minutes, cool- ing, adding 30 c.c. of alcohol, and filtering. Of this concentrated solution 5 c.c. are taken and made up to 500 c.c. at 60° F. As the catechu-tannic acid in the catechu combines to form an inky compound with iron, it is important that every trace of the latter be removed from the paper before toning. THE CARBON PROCESS. 109 CHAP TEE X. The Bichromate Printing Processes, All that can be told about the chemistry of the bichromate processes, so far as it is known, can be said in a very few words, the subsequent applica- tions of this knowledge being purely mechanical There are two chromates of potassium, the normal yellow chromate (K 2 Cr 04 ), and the acid orange chromate (K 2 Cr. 207 ). When the latter is mixed with a colloid organic substance (see p. 113) and exposed to light under a negative, two important changes are noticed : the organic matter is rendered comparatively insoluble where the light has acted, and the material has lost its power of absorbing water and becoming sticky, or “ tacky.” On these facts the whole of the bichromate processes depend. In the carbon process, carbon, Bartolozzi red or some other colouring matter is incorporated with gelatin, and made into thin sheets of “ tissue,” which, about twelve hours before use, are sensitized by immersing in a 5 per cent, solution of potassium bichromate for three minutes in winter and two in 110 CARBON TISSUE. summer, at 60° F. It is then hung up to dry in the dark. The exposure is made under a negative, the time required being judged by means of an actino- meter. After exposure, the tissue is transferred from its own paper to another paper prepared specially beforehand by coating with Nelson’s No. 1 gelatin, . . . J oz. Water, ...... 10 ozs. Allow the gelatin to soak for an hour in the cold water, and then dissolve in a water -bath. When dissolved, stir in half a dram of formalin. Brush well over the surface of the paper, and allow to dry. The object of this is to make sure that the tissue will stick fast when squeegeed on to the paper. The transfer paper is soaked in water for a time, which varies according to the thickness of the paper. The tissue is then placed in the same water with the prepared paper, and when the tissue begins to flatten, the two are lifted from the water together, being then squeegeed into close contact by means of a flat squeegee. After being pressed be- tween blotting boards, the whole is immersed in hot water at about 110° F. As soon as the gelatin begins to soften round the edges, the original sup- porting paper is removed. The back of the sensitive gelatin film is now uppermost, the surface on which the light has fallen being beneath. Where the light has acted SINGLE AND DOUBLE TRANSFER. Ill strongly the gelatin is insoluble nearly right through, but in the parts corresponding to the black parts of the negative only a thin film is insoluble. By washing the film from the back, which is now uppermost, the soluble portions will be washed away, leaving a sort of raised map, the hills corre- sponding to the light parts of the negative, and the dales to the dark portions. Where the gelatin be- comes insoluble it entangles and fixes the colouring matter, so that a print in monochrome with all the gradations of the original is produced. The method just described is that of single trans- fer, the right and left of the original subject being reversed. In some cases this is objectionable, so the tissue is developed on a temporary support, con- sisting generally of opal glass, coated with the fol- lowing : — Pure bee’s-wax, . . . . 2 drams Yellow resin, . . . . . 6 „ Turpentine, . . . . .1 pint any excess being removed by polishing with a cloth. Paper coated with a film of partially soluble gelatin, to be used as a final support. Before use, a sheet is soaked for half-an-hour in a 2 per cent, solution of alum, and then placed in water with the supported tissue, which should be transferred in the manner described under single transfer. In both cases the development should be carried out with warm water, the temperature of which 112 , ARTIGUE PAPER. can be varied according to the correctness of the exposure, higher temperature being employed for under-exposed prints. After development, they should receive a final wash with cold water, and should then be soaked in a 5 per cent, solution of alum until all bichromate stain has been removed, when a final rinse with cold water is given. The development vshould be carried out as soon as pos- sible after printing, as the action once started by the light continues automatically in the dark. It is advisable to “ safe edge ” the print before exposing by protecting the margin of the negative from the light by means of black paper. All who are inter- ested in carbon printing should read J. A. Sinclair’s excellent monograph, from which the above formulae have been taken. It appeared together with other valuable and interesting papers on the bichromate processes in the Journal of the Royal Photographic Society for May 1896, the set of papers being sub- sequently published by Dawbarn & Ward, Ltd. A very beautiful process for carbon printing without transfer has been revived recently, and is known as the Artigue or bichromate gum process, an account of which will be found in Mr Sinclair’s paper. Instead of gelatin, a warm black pigment is worked up with gum, and coated on paper. This is sensi- tized in a 2 per cent, solution of bichromate of potash, and exposed under the negative without a “ safe edge,” an actinometer being employed as in the ordinary carbon process. In development, the HALF-TONE AND COLLOTYPE. 113 paper is first treated with warm water, and then with a mixture of warm water and fine sawdust. After development is complete the paper is soaked in a 5 per cent, solution of alum, and then washed in cold water. In the half-tone process of reproducing photo- grams and tone drawings, a copper, or sometimes a zinc, plate receives a coating of gelatin or other colloid, which is sensitized with bichromate. This is exposed under a negative made from the original through a cross line or other screen which breaks up the tones into dots. After printing, the plate is developed by washing, and etched with ferric chloride or an acid. There are various modifica- tions of this process, all depending on the action of light causing the gelatin to become insoluble. For details of these processes other works should be consulted. In collotype, advantage is taken of the fact, pre- viously mentioned, that when bichromatized gelatin is acted upon by light it loses its tendency to absorb water, and becomes tacky. After printing under the negative, the sheet of gelatin is fixed on the press, and kept moist. Where the light has acted, the surface takes the ink in proportion to the amount of light that has fallen upon it. Several other processes depend upon this selective action of the gelatin as regards greasy ink. Glue, fish-glue, size and isinglass are all forms of gelatin. They are colloids, i.e., they will absorb H 114 ASPHALTUM. water to an indefinite extent, but do not pass through animal membranes, such as bladder, as a solution of salt, sugar, or other crystalloid substances would do. For photographic purposes, gelatin should contain little ash — not more than about 3 per cent. — should take up from five to ten times its weight of water when soaked in the cold, and suf- ficient to dissolve it on warming to 85° F. In the common line-engraving process, asphaltum is generally used as the sensitive substance. This asphaltum or bitumen is obtained from deposits of pitch in different parts of the world. It has a pecu- liar smell, and resembles the heavier portion of gas tar. It is partly soluble in alcohol and ether, more so in benzene and essential oils, and dissolves com- pletely in chloroform, carbon bisulphide, and mineral oils. Caustic alkalis dissolve it ; hot sulphuric acid dissolves and decomposes it, but nitric acid is without action upon it. Asphaltum is sensitive to light, and is obtained in best condition by exhausting with ether, the insoluble portion being dissolved in benzene. A plate is coated with a varnish of this material, and exposed to light under a negative or transparency, being developed with a mixture of benzene and turpentine, which dissolves off the bitumen that has not been rendered insoluble by light. The plate is then etched and treated in various ways. LIGHT FILTERS. 115 CHAPTEK XL Orthochromatism. Light does not affect an ordinary gelatino-bromide emulsion in the same manner as it does the eye. The latter is most sensitive to the yellow of the spectrum in the neighbourhood of the sodium or D line, but the violet and ultra-violet part of the spectrum has the greatest effect on a gelatino- bromide film. To remedy this defect, yellow or yellow orange light-filters are introduced, either in front of the lens, or between the lens and the plate. The effect of this is to cut off the violet end of the spectrum to a greater or less extent. The author has investigated a large number of these filters, and has found considerable variations in their absorptive powers. As a general rule, the gelatin or collodion filters should be avoided, as the colour- ing matter in this form has a great tendency to fade. The filters made of flashed glass are the most satisfactory. The question of what filter to employ is a very difficult one, as the action depends so largely on the strength of the light. It is un- 116 SENSITIZERS FOR DIFFERENT RAYS. fortunate that no standard light-filters have yet been fixed upon for iso-chromatic work. In addition to this means of modifying the light before reaching the plate, it has been found that certain organic dyes have an important influence on the absorptive power of the silver salt for the different parts of the spectrum. The undyed gelatino-bromide plate is most affected by the blue rays, the action of the green and red on the plate being very small in comparison. In a plate dyed with ammoniacal eosin, the action, although still greatest in the blue and about the same in the violet, extends right up to the yellow green, falling away rapidly, however, at this point. Ammoniacal erythrosin renders the action com- paratively uniform from the green-blue to the end of the visible violet. In the green-blue there is a rapid falling-off, as is the case with eosin, followed by a rise in the green, the maximum action being reached in the yellow instead of the yellow-green as with eosin, and the action extends with lessen- ing effect right through the orange. Ammoniacal rose Bengal gives a very similar effect, but the maximum is in the yellow-orange and extends further into the red. Ammoniacal cyanin has its maximum effect in the red. Speaking generally, rose Bengal is the best sen- sitizer for the yellow green, and cyanin for the red. A solution of one part of the dye in ten thousand of water is a convenient strength to use, one part COLOUR SENSITIZERS. 117 of ammonia being added to each hundred parts of water or alcohol. After soaking the plates for two minutes in the solution of the dye, they are washed to remove the excess of dye, and dried before exposure. As a rule, orthochromatic plates lose their sensitiveness and go wrong more rapidly than ordinary plates, and should be used as soon as possible after manufacture. They tend also to fog if forced in development. These drawbacks, how- ever, are, as a rule, insignificant compared with the advantages gained in colour correctness, and it is only under trying conditions, such as long storage, that these defects interfere seriously with the use of the plates. The brands of colour- sensitized plates now in the market are a great improvement on the early orthochromatic plates, and possess better keeping properties. Coerulein, alizarin blue, and other dyes are used as sensitizers for the red, besides those mentioned. 118 CHEMICAL PURITY. CHAPTEE XII. IMPUPJTIES AND SUBSTANCES THAT ALTER IN THE AIR. It is extremely probable that no substance has ever been obtained chemically pure. Xo one who has not occupied himself in chemical research or read the memoirs of those who have done so can have any idea of the almost insuperable difficulties to be encountered in obtaining a substance in a state of purity. In fact, the word “ pure ” as applied to chemicals is entirely comparative. It is impossible to obtain pure water, for instance, in glass vessels and in the air, as the water attacks and dissolves out the alkali from the glass on the one hand and dissolves air on the other. Distillation in platinum vessels in a vacuum is the only method of obtaining water in the pure state, and then the purity is probably far from abso- lute. Consequently, “ pure ” in a chemical dealer’s list means freedom from any gross impurity. For many purposes the “ commercial ” variety of che- mical answers quite as well for photographic pur- poses as the pure,” but there are instances in which it is necessary to guard against some par- IMPURITIES IN WATER. 119 ticular impurity , and these cases are indicated below. Water, as ordinarily supplied from the tap or the weU, is a very impure material. Apart from actual suspended matter, well or spring water contains varying quantities of carbonate and sulphate of lime and magnesia, phosphates, nitrates, chlorides — generally of sodium — and a certain quantity of ammonia. Surface water usually contains more ammonia, not much lime and magnesia, but a certain quantity of peaty matter. Eain water is fairly pure unless the roof from which it is collected is particularly dirty. Occasionally a water contains iron, and there are rarer impurities which need not be considered here. The worst impurity from a photographic point of view is chloride, which reacts with silver nitrate to form insoluble silver chloride ; excess of lime or magnesia is often objectionable, particularly where oxalates are used, as insoluble oxalates of lime and magnesia are formed ; iron is, of course, fatal, but does not often occur ; peaty matter is objectionable as it stains printing papers. All these impurities may be removed by distilling the water, rejecting the first pint that comes over as it contains nearly all the ammonia. Boiling is sufficient to precipitate the carbonates of lime and magnesia, or temporary hardness, but the sulphates, or per- manent hardness, still remain. Commercial sulphuric acid contains lead and other impurities. Acid of good quality is so cheap 120 IMPURITIES IN ACIDS AND ALKALIS. that it should be used for all photographic purposes. It should not be exposed to the air as it absorbs water rapidly, and in diluting, the strong acid should always be added to the water instead of vice versd, as great heat is developed. Commercial hydrochloric acid or muriatic acid invariably contains iron. Photographers should avoid an acid that shows any trace of yellow. Alkalis, whether caustic or carbonate, contain various impurities. It is well to filter the solutions, when making up concentrated developers, etc., through a plug of asbestos or glass wool, or to allow the solution to stand and decant off the clear portion. Alkalis act strongly on the glass of the bottles con- taining them, and a clear solution generally has a deposit at the bottom after awhile. Alkalis should never be kept in stoppered bottles, as the stoppers become hopelessly fixed after a short time. Cyanide of potassium deteriorates somewhat rapidly owing to the carbonic acid of the air turning out the prussic (hydrocyanic) acid. Old cyanide should never be used, as it probably contains nothing but carbonate. See that the cyanide you buy has not been in the shop for a long time ! Sulphocyanide is very hygroscopic, i.e., it absorbs water from the air. For this reason it is best to convert it into, say, a 10°/^ solution as soon as possible after purchasing. Sulphites and bisulphites should be kept in stoppered or well-corked bottles, which should not IMPURITIES IN IRON SALTS. 121 have a large air space above the crystals, as the air oxidizes them rapidly to sulphates, in which condition they are useless to the photographer. Thiosulphate (“ hypo ”) as usually sold is pure enough for the photographer’s purposes. When making up a solution care should be taken to neutralize any acidity with a little ammonia or sodium bicarbonate. Thiosulphate solutions oxidize readily in the air, and fixing baths become acid on keeping. (See also page 73.) Ferrous sulphate contains more or less ferric salt, due to oxidation, and any crystals that show a yellow or brownish tinge should be picked out and thrown away. Some chemists keep pieces of metallic iron at the bottom of their solutions of ferrous sulphate, but a better plan is to fill a number of small bottles quite full, cork them, melt up some paraffin candle ends, and dip the tops of the bottles into the paraffin for a few moments. In this con- dition the contents of the bottles can be kept from the air until required. If the ferrous sulphate solution be put into a large bottle, air is admitted every time the stopper is taken out, and the air space above the solution gets larger as the material is used, so that deterioration goes on at an increasingly rapid pace. Ferric chloride nearly always contains free hydrochloric acid and sometimes ferrous chloride, but this is not usual. For etching purposes the presence of free hydrochloric acid is an advantage, 122 IMPURITIES m SILVER AND GOLD. SO long as there is not too much of it. Neutral or nearly neutral ferric chloride has a tendency to deposit basic salts, Le., compounds of oxide and chloride, and this should be guarded against. If too acid, the resist may come away from the plate when etching. Only experience can tell the etcher when his bath is in the right condition. If it shows a tendency to deposit, a little hydrochloric acid should be added ; if too acid, it is well to add a little ferric hydrate, kept for the purpose and made by adding ammonia to ferric chloride solution, allowing the jelly to settle as far as it will, decanting off the clear portion, adding hot water, and again decanting. Silver nitrate is generally pure, but does occasion- ally contain copper, which can be detected by the colour of the solution. It is necessary to keep all silver salts from the light, as they darken and spoil. Gold chloride, as obtained commercially, contains hydrochloric acid, which requires to be neutralized with a little chalk or whiting. Instead of the pure salt the double chlorides of gold with sodium or potassium are often sold. These are quite as convenient for photographic purposes as the pure chloride, and so long as the photographer gets his proper quantity of metallic gold, it is of no conse- quence whether it is in the form of pure chloride or not. RECOVERING SILVER. 123 CHAPTEE XIII. Eecovery of Eesidues. The waste gold, silver, and platinum salts contained in used up fixing- and toning-baths, spoilt sensitized paper, etc., are often saved and treated for the recovery of the metals. It is rarely worth the while of an amateur to trouble about saving his residues unless he works on a very large scale, but it is a matter that should not be neglected by the professional photographer. The fixing-baths, satur- ated with the double thiosulphate of silver and sodium, are most worth attention. Every five ounces of “ hypo ” is capable of taking up about two ounces of silver, and although the saturation point is never reached in ordinary practice, yet fixing-baths that have had a large number of plates and papers passed through them do contain a considerable pro- portion of silver. The old fixing-baths are thrown into a tub with a solution of “ liver of sulphur ” — a complicated mixture of sulphides and other things obtained by fusing sulphur with potassium carbonate — which precipitates the silver as sulphide. When the tub is nearly full, a sample should be taken in a test-tube or small vessel, and a few drops of liver of sulphur solution should be added to it. If no 124 SILVER AND GOLD RESIDUES. precipitate forms, all the silver has been deposited ; if the liquid turns brown, more liver of sulphur must be added to the tub. When the deposit has quite settled, the clear portion of the liquid should be drawn off through a tap in the side about a foot from the bottom. In time the sludge of silver sulphide will reach the level of the tap, when the cask should be emptied by running it out through a hole at the bottom, closed in the ordinary way by a wooden plug. Underneath the hole at the bottom of the cask, a large glass funnel con- taining a rag or filter should be placed, and the sludge should be run on to this : the liquid portion filters through, leaving the solid silver sulphide on the filter. It should be allowed to dry and then labelled “ silver sulphide ” and sent to a refinery to be reduced. Scraps of sensitized paper, gelatino-chloride, bromide, and other papers should be burnt to an ash, and forwarded to the refiner. Toning-baths are treated with solution of ferrous sulphate, which reduces the gold to the metallic state. The reduction of the silver is performed at the refiner’s by fusing the sulphide, etc., with red lead, etc. ; the resulting button of lead contains all the silver. The button is heated on a cupel or dish of bone-ash in a current of air. The lead is oxidized to litharge (PbO) which sinks into the cupel, leaving the silver behind. CELLULOSE AND VISCOSE. 125 CHAPTEE XIV. Cellulose. Cellulose is the essential constituent of all the hard parts of plants, and its usefulness to mankind in general, and to the photographer in particular, is almost unlimited. Jute, hemp, paper, linen, cotton, etc., are all more or less pure forms of cellulose. Schleicher and Schull’s filter-paper is pure cellulose, whilst cotton-wool and ordinary blotting-paper con- tain very little foreign matter. Pyroxylin, or gun cotton, is a nitrate of cellulose, and collodion is made by dissolving this in suitable solvents. Cellulose belongs to a large family, which, besides several closely allied forms of cellulose itself, includes starch, cane-sugar, grape-sugar, dextrin, and other bodies. They are all known in chemistry as carbo-hydrates, because they contain carbon and hydrogen and oxygen in the proportion to form water. Although their percentage composition has been known accurately enough for some time, the actual way in which they are built up is still being worked out, and although the materials out of which they are built 126 WILLESDEN PAPER. are so simple, the actual structure is very com- plicated. Cellulose, for example, is generally written (CeHioO^)^, which means that chemists do not yet know how many CgHioOg’s go to make up a complete molecule of cellulose. The same is true of starch and dextrin. Celluiose is soluble in strong sulphuric acid, being converted into glucose or grape sugar, but if paper be passed through dilute sulphuric acid of specific gravity, 1’5, it is parchmentized. Copper sulphate precipitated as hydrate of copper by ammonia sol- ution, and dissolved in excess of the latter, forms the usual solvent for cellulose. Advantage is taken of this solubility in cuprammonia solution in the manu- facture of “ Willesden ” paper. Thick paper is treated with the solution, which gelatinizes the surface, rendering it more resistant and waterproof. For roofing and similar purposes, two or three sheets of the paper are cemented together by the solution. Strong alkalis and zinc chloride disintegrate cellulose after a short time, but alkali of moderate strength, such as 15 per cent, solution of caustic soda, com- bines to form alkali-cellulose, adding considerably to the strength of the material. This treatment with 15 per cent, alkali is known as “ mercerizing.” About three years ago, Messrs Cross and Sevan discovered that if this mercerized cellulose be treated with carbon bisulphide a soluble xanthate of cellulose is produced. This compound, which the inventors term “ viscose,” has PYROXYLIN. 127 almost endless applications, many of which are of great interest to photographers, the important point about it being that from its solution in water, the cellulose can be recovered almost chemically pure. The solid “ viscoid,” made by coagulating viscose, closely resembles “ celluloid ” (see below), and can replace it for many purposes, having the advantage of being practically inflammable. By treating cotton-wool with nitric acid, various nitrates are formed. To secure good results it is necessary to have the nitric acid perfectly dry. As this is difficult to obtain in practice, a mixture of nitric and sulphuric acids are used, which produces the same effect as if perfectly dry nitric acid alone were employed. Three fluid ounces of nitric acid (sp. gr. 1429) are mixed with two fluid ounces of water in a large beaker- flask, and nine fluid ounces of strong sulphuric acid (sp. gr. 1839) are run into the mixture with constant shaking round. One hundred grains of dry cotton-wool divided into about ten pieces are dropped into the solution when its temperature has fallen to 150° F., and allowed to remain for 7 or 8 minutes, when the acid is drained off, the cotton being squeezed with a glass rod to squeeze out as much acid as possible. It is necessary to wash the cotton thoroughly to remove every trace of acid, when it may be dried in the air. This gun- cotton, or pyroxylin as it is often called, is soluble in a mixture of alcohol and ether, but they must neither of them be methylated. The follow- 128 CELLULOID. ing are convenient proportions for making plain collodion : — Pyroxylin, . .1*2 grams, . 60 grains. Alcohol (*820) . 50 c.c., . 5 02 s. Ether (’725), . . 50 „ . 5 „ In winter it is convenient to use 5 c.c., or half an ounce more ether and the same quantity less alcohol. The formula for iodized collodion will be found on page 43. Celluloid is a mixture of tri-nitro cellulose with camphor, and xylonite is a somewhat similar material. Other substances are added to reduce the inflammability of the first-named materials. Paper can be tested for acid by pulping a con- venient amount in a beaker-flask with a little boil- ing water, and adding one drop of alcoholic solution of methyl orange. If it turns red, acid is present. A dilute solution of iodine in potassium iodide is used as a test for hypo.” The amount of loading is ascertained by burning a given quantity of the paper to an ash and comparing with an equal weight of good filter-paper, treated in a similar manner. COLOPHONY AND LAC RESINS. 129 CHAPTEE XV. RESINS, VARNISHES, ETC. The resins form a large class of complicated organic substances, found principally as exudations from trees in nearly all parts of the world. They are soluble as a rule in alcohol, ether, and benzene, but are insoluble in water. Photographers use them in making varnishes and in laying a dust ground in photogravure. The resins of most importance in this connection are colophony or common resin, lac, mastic, dammar, sandarac, dragon’s blood, anime, copal, amber, caoutchouc and gutta-percha. Colophony is obtained from pine trees in Georgia, U. S. A., and the Landes district in Prance. It varies in colour from pale yellow to dark red-brown. It is soluble in nearly all organic solvents and in hot linseed oil. Heated with caustic soda or potash it forms a resinate, which is an important con- stituent of yellow soap. Specific gravity 1'07. Lac resin is produced in many East Indian trees, through the exudation of juice, caused by the bite of an insect; the red tint is due to the colour of the I 130 MASTIC. insect itself. The small branches with the resin on them are known as “ stick lac.” When the resin is removed, it is called “ seed ” or “ grain lac,” and, when melted by boiling water and run into thin layers, as “ shellac.” The dye removed by boiling is known as “ lac dye.” The specific gravity of the resin is about 1*12. This resin is soluble in all the usual solvents, and in dilute hydrochloric and acetic acids, and in caustic alkalis. By treatment with chlorine bleached lac is made. After bleaching, it should be kept under water, being dried shortly before use, as exposure to the air soon renders it insoluble. The freshly bleached lac forms a nearly colourless solution in alcohol, and is soluble in a hot solution of borax and in sodium carbonate. In a mixture of the last two solvents, it forms a water varnish, sometimes used for negatives, etc. An excellent waterproof ink can be made by rubbing up Indian ink with a solution of lac in borax (water, 1 oz ; borax, 130 grains; freshly bleached lac, 100 grains; sodium carbonate, 6 grains.) Ordinary alcohol contains at least 5 per cent, of water, and as the alcohol evaporates in the cold faster than the water, the latter is left behind, dulling the surface of the lac. If heat be applied, however, the alcohol and water are driven off together, leaving a bright surface. This difficulty is not met with if the lac or other resin be dissolved in chloroform or benzene, which can be used cold. VARIOUS RESINS. 131 Mastic or mastiche is obtained from an evergreen shrub on the shores of the Mediterranean. It occurs in pale yellow transparent “ tears/’ is brittle and sweet-smelling, melting at about 226° F. Alcohol or warm acetone dissolves it freely, and it is partly soluble in hot linseed oil, precipitating slightly on cooling. Specific gravity 1*07. Sandarac exudes from an evergreen tree in N. Africa, and somewhat resembles mastic. It has a specific gravity of 1’04 and dissolves readily in the usual solvents, including hot linseed oil. Dragon’s blood is obtained as a blood-red exuda- tion from the rattan palm. It dissolves in most of the usual solvents and in caustic soda and glacial acetic acid, but is insoluble in petroleum ether, (benzine, or benzoline), and but sparingly in ether or oil of turpentine. There is a good deal of variation, however, in its constitution and properties. It melts at about 250° F. and has a specific gravity of 1197. In photography it is used as a resist when etching metal. Elemi contains a large proportion (12j per cent.) of volatile oil, is pale yellow in colour, and of various origin. It is very fusible and is used to give tough- ness to lacquers and varnishes. Elenii is often adulterated, or a factitious product, consisting of colophony, Canada balsam, and essential oils is substituted for it. The fraud may be detected by heating, when, after a short time, the turpentiny smell of the common resin is unmistakable. 132 RESINS AND BALSAMS. Dammar is obtained in lumps of varying size from pine trees in the East Indies. The fossil Kauri gum found in Kew Zealand, etc., forms another kind of dammara resin. It is not very soluble in alcohol, more so in ether and completely so in oil of turpentine, petroleum ether, etc. ; it dissolves also in hot or cold solutions of sodium carbonate. Its specific gravity is about 1*05. Anime and copal are obtained from various sources, some of them fossil, the latter being highly prized. The S. American resin is generally known as “ animi ” and the East Indian as “ copal.” Some of the East Indian copals are soft and are soluble in ether. Hard copal is light-brown in colour and makes excellent varnish. Its specific gravity is generally between 1’06 and I'O?. Before being heated, copal is insoluble in alcohol, and only slightly soluble in ether or oil of turpentine. On heating, however, gases are given off, and the residue dissolves readily in ether and oil of turpentine. Amber is a fossil resin, largely used for orna- mental purposes. It is insoluble in alcohol, essential oils and in acids, with the exception of sulphuric acid. The specific gravity of amber varies from 1*05 to ITO and its melting-point is 550° F. Like copal, it is changed by heat, and is then soluble in alcohol and turpentine oil. The balsams are resins containing varying pro- portions of essential oils and similar substances. Among these oleo-resins, Canada balsam is of INDIA-RUBBER. 133 importance to photographers. It is a pale yellow, transparent material, which forms a beautifully clear, glassy varnish. Canada balsam dissolves in benzol or chloroform, and is much used in this state as a medium for mounting microscopic objects. ' Caoutchouc, or India-rubber and gutta-percha, are often confused, but they are quite different sub- stances. Caoutchouc is a complicated body containing several different chemical substances, and varies a good deal in its properties according to its place of origin. It is soluble in coal-tar naphtha, ether, chloroform, bisulphide of carbon, benzene, and oil of terpentine. Its principal use in photography, besides india-rubber tubing, vulcanite dishes, etc., is for safe edging plates. Sulphur combines with caoutchouc, the product — vulcanite — being insoluble in any solvent, not affected by heat or cold, much more elastic than caoutchouc, and generally more permanent. As this is a somewhat miscellaneous chapter, it is convenient here to say a few words about oils, and solvents. Oils may be divided into mineral oils, fixed oils, and essential oils. Essential oils nearly all possess the formula CioHig; they are very volatile and possess strong odours, which are some- times due, however, to the presence of other volatile materials, such as cinnamic aldehyde in oil of cassia, benzoic aldehyde in oil of almonds, etc. Oils of turpentine, lavender, cloves, peppermint, etc., are examples of essential oils. They possess strong solvent powers, especially on resins. 134 OILS AND SOAPS. The fixed oils are of vegetable and animal origin, and consist principally of mixtures in varying pro- portions of oleic, palmitic, stearic, and similar acids combined with glycerin. Alkalies combine with the acids, setting free the glycerin, and this is what happens when soap is made, soap being oleate, palmitate, stearate, etc., of soda or potash. Hard soaps contain soda, and soft soaps, which are generally manufactured from fish oil with a little oil of almonds to cover up the fishy smell, contain potash, but mixtures of soda and potash are often employed. Most soaps are more or less adulterated with silicate of soda, aluminate of soda, talc, etc., and water. Yellow soaps contain resin ; unless in excessive quantity, however, this should not be considered an adulterant. Free alkali is often present, which is objectionable for most purposes except scouring. The drying oils contain linolic and linoleic acids, which are acted upon rapidly by oxygen if exposed to the air, a skin being formed which acts as an excellent waterproof varnish. Advantage of this property of drying oils is taken in mixing paints ; it is not the colouring matter of the paint but the drying oil that affords the protecting surface. Lead salts assist this drying action, and a white or red lead paint dries very rapidly and forms an excellent protection against weather. The principal drying oil is linseed, the following oils, however, possess drying properties to a less extent : hemp, walnut, poppy, and sunflower. SOLVENTS. 135 Castile soap should be made from pure olive oil. Once upon a time Marseilles soap was made from olive oil, and some of it may be still, but the greater portion of the Marseilles soap in the market is made from all kinds of oils. Beeswax is the principal wax employed, but it is adulterated with paraffin, Carnauba wax, and Japan wax. Paraffin is used largely as an adulterant, and may be detected by treating the wax with oil of turpentine, which dissolves the beeswax and leaves the paraffin. As regards solvents, two of importance are fre- quently confused : hQuzene and benzme are quite different bodies. The latter is light petroleum oil, sometimes called petroleum ether, whilst the former is the active constituent of coal-tar naphtha. Crude paraffin or petroleum oil contains a whole series of bodies known as paraffins, the lowest of which are gases — marsh gas (CH4), ethane (C2Hg), propane (CgHg), butane (C4H10) — then come volatile liquids, beginning with pentane (C5H42), each member of the paraffin series differing from the next by CH2, then the burning oils, then the heavy oils — solar distil- lates, used for enriching water gas — then the vaselines, then the lubricating oils, and at last solid paraffins or paraffin wax. Benzine or benzoline consists of the paraffins following and including pentane ; all the liquid paraffins, however, possess strong solvent powers for grease, resins, and many other substances. 136 ALCOHOL AND ETHER. Benzene is obtained by refining light coal tar oil and is perhaps the most important compound known to chemists. It contains six atoms of hydrogen united to six atoms of carbon, and acts in all its properties and derivatives as if it were joined into a six-sided ring, as shown on p. 57. It is some- times called benzole. Chloroform may be considered as marsh gas (CH4) in which 3 H’s have been replaced by 3 Cl’s, its formula being CHCI3. It possesses great solvent powers, especially for fats. By Alcohol is meant ethyl alcohol. The alcohols form a series in the same way as do the paraffins, being derivatives of the paraffins. For example, ethane, by a round-about chemical process, can be converted into ethylic alcohol, thus : Ethane. Ethylic iodide. Ethylic alcohol. CH3.CH3 CH3.CH2I CH3.CH2OH. From ethylic alcohol, ethylic ether or “ ether ” can be obtained by removing a molecule of water with sulphuric acid. By oxidation, alcohol is converted into aldehyde (CHo.COH), and by further oxidation into acetic acid (CH3.COOH). Ethylic alcohol. SOLVENTS AND VAENISHES. 137 From acetic acid another solvent, acetone (CH3.CO.CH3) is obtained. It is a powerful solvent of most organic substances. Methylated spirit has crude wood spirit added to it for the purpose of making it undrinkable, so that the material, as sold, contains ethylic and methylic alcohols, besides acetone and various resinous materials. It is interesting to note that pure methylic alcohol is the lowest of the series, being based on marsh gas (CH4) in the same way that ethylic alcohol is based on the next member of the series, ethane. By similar treatment to that given above, methylic alcohol, methylic aldehyde or formic alde- hyde, as it is usually called, and formic acid are obtained. Carbon bisulphide is a compound of carbon and sulphur (CS2). It is used principally as a solvent for india-rubber. The following are useful formulae for varnishes : — Amber Varnish {Abney). Fused amber (powdered), . . 1 part. Chloroform, . . . . .16 parts. May be used cold for plates or prints. Collodion Varnish {Gamble). Pyroxylin, ... 2 grams, 100 grains. Ether (methylated), . 50 c.c., . 5 ozs. Alcohol (methylated), . 50 „ . 5 ,, Castor oil, . . . 0'3 ,, . 16 minims. 138 VARNISHES. Varnish for Collodion Lantern Plates {Photogram). Dammar, ..... 1 part. Benzole, . . . . .20 parts. This varnish can he used cold. Lac Varnish {Cooley). Seed Lac or Shellac, ... 4 parts. Rectified spirit, . . . . 20 „ Clear Mastic Varnish {Phoiogram). Mastic, Canada balsam, . Sandarac, . Oil of turpentine. 14 ozs 2 „ 6 „ 44 „ Shake, and stand till clear ; filter. The mastic, sandarac, and turpentine oil must be dry. The longer it is left before use the better. Gold-Colored Lae Varnish {Cooley). Ground turmeric, . . . . J lb. Rectified spirit, . . . .1 gall. Macerate for a week, strain, and squeeze off, and add — Gamboge, . . . . . f oz. Pale shellac, . . . . .6 ozs. Sandarac, . . . . - If Ihs. When dissolved, strain, and add further of turpentine mastic varnish (last formula), 1 pint. This varnish is suitable for picture frames, brass and other metal work. The colour can be altered as desired by varying the constituents. By substi- tuting dragon’s blood for gamboge, a deep gold VAKNISHES. 139 coloured varnish is obtained. It is a good plan to keep the colouring matters separate in concentrated solutions and add them as required. By using annotta instead of turmeric, and dragon’s blood instead of gamboge, a red varnish, suitable for wood, is obtained. Ordinary Spirit Varnishes (Thorpe). I. Brown hard — Sandarac, . . . . .3 lbs. Pale shellac, . . . . . 2 ,, Methylated spirit, . . . .2 galls. Dissolve and add 1 quart turpentine mastic varnish. Agitate well, strain through gauze, and after one month decant off clear portion. II. White hard — Sandarac, Camphor, Pounded glass. Methylated spirit, . 5 lbs. 2 ozs. 3 lbs. 7 quarts. Dissolve, and when strained, add 1 quart pale Canada balsam. All the above are “ spirit ” varnishes. An “ oil varnish” contains a drying oil in addition to the resin and other constituents. The following is a good oil varnish suitable for wood-work, etc. — Pale hard copal, . . . .2 lbs. Fuse and add Hot boiled linseed oil, . . .1 pint. Boil until stringy, and thin with about 3 pints oil of turpentine. OTOLOP^DIO INDEX, 140 cyclop.^:dic index. s § § s rC) ■>. k-i d ^ S & tn w > “ > CO c/j § CO O |> > ^ > CO OOO (M-i ^ CS o 2 .2 ‘5^ ffi 05 +3 ._4 C 2 <-H " .2 “ o ^ S'® ^ , W . S ^ o t- 2 "-S -ss i -sg 05'' rH m :=J • o • .2.2 '3 O O r2 .2 'p< '-M .2o'^ fc-.^ '05 .2 rt '3 "o o ® M ’-^ 05 in 2 2 2 o .2 ‘3 .2 2 2 ‘C o .2 o - 0^3^. 'Soc^ ■S3 pquQOOPi^^O W W WW!^ C5 a ^ S • M -c ^ > o 00 a d T3 . . o . o . . flCOOajM . . .o ' c a • C 1-1 ® >• c ^ c*3r^'®oo^ .ooco^^cocMO ooo^Jf^-^coco ^ I— o> o» 05 O O 05 CM 05 05 05 05 o w" o” «0 « C<) rf ?? OO +Offi X, X WW QK + (M ‘ ^.is tew teo te ' o3 o g a o . w a|^ ^ 'a ^ S M g M s'^.a a fl ^ o o o ,o w w ' • a CO CO i-( CO CO o CO CO CO 05 (M ^oo CO Tji ^ o- 00*' (>J § CO CO (M CO t-l T o :z ra :s ; - ... .a a> =D >1^ pO a ci ^ .-^ cn o O O-0 j”.3’7^+^ 5>. p3 O 5h r!^rX O ^ 2 C5 WoSphc^mkEhh 8 W a '--.a ^ Ja ■^l-S .-I ' — ce o3 2 O .2 rs P-i O . CO a o I c3 O A- i 'a 'a i ' O O c s a ‘ a a 142 CYCLOPAEDIC INDEX. ■e Cold lcoh( M CO g ^ M . lO CO . . . C<) Tj< M CO • Pk o fed a Boilin Watei 422 vs. dec. 73 vs. VS. vs. vs. s. vs. 200 'o Cold Water. _ 00 lO lO M . ^ (N CO ►> 165 200 33 s. 105 <^ . . . 130 Molec- uJar Weight. 253 98 175 52-5 37 35 145 80 143 51 76 124 CO • • CO CO o Symbol. o', o W ffi ::a H? £• S . • OT • . . r-> • CO OT CO W . CO . VO oo CO o • ^ n3 >• I— I rH CO 40 vs. i. i. • CO w . w 1-06 160 90 o . 1 — 1 132 0-137 ss. rfH lO Oi no '5ti (M oH • 05 «0 o o 05 ^ « ' ' ■ r-H . o o T-H CO c^ Tj< CO i-H ^ CO CO CO CO l-H CO r-H _ O 9.0^ w a oo , oo w w M CO O ^ j_ C« CD +?i?« Br CO (N + +!^ ^ O ^9 ?oOo (nOPCO r ^ ^ O r*^ CQO t; QO o • • Cfl • • • -M rfi rQ ^ § cd eg ^ ^ • • qJ q5 • • II &£ .2 +5 • ' __ 3 oT-^ S ^ rO T5 •5 --I o o o ^ p ^ ;s a> IB — A- 05 ^ JJC Crystallise Benzole . Benzoline •jili III! <50 . Co Cq Cq Cq • • § ' ' .::i § ^ . .^>2 CQ . . rO . . . ^ •S Chalk, ' ■ plaster Slaked lim Chloride o Bleachin »o Tt( o Tt< • • • • CO (S'~' o 22 o-t2 O oO „ CO .. 2 -05 .,05 ^ 05 IT5 =C) O O rH 611 o • • o3 3 o £ * ® CD -U 3 T 5 • ■ ce 'x ® 0.'^ O S=S’S.2i.SSi . ■=.2KdiSS-S i'- 03 .r< 5^:2 o q:> ® (u .— WPQWPQ QJ 'X3 . . . 144 CYCLOPEDIC INDEX. •1 1 o 2 ° -H O O CQ *f4 * . « ' • • « 1 Ph ■< o bo o C >> Boilin Water 450 • ••- • • • 2 o CO Cold Water 200 • -* • • • . . . o ^ o3 bO d ci oo o cc o c o o 5^ a . cfl O • ^ CO CO 09 . . .» >p 'P -p. 0 CO 0 OS S 0 (M ^ (M (N i-H (M 10 iG INDB^. 00 ^ CO § coco^w^o -?0 »0 «o 'TJ a o a o |.S » t-i c 2 3 >> O QOQ g 5 9 °3 ^ to a POP 5 ^- 3 SU . 2 . a -^ ^^-§3 fl 03 O ce d o 2 § ft « . 03 d o 2.5 .3 ^ s] cr* (S O 03 03 PP I-I '-' Sh d o nj.rrt d^ I — I f— 1 03 03 ^ a ® 1-^ PnPL(t>> ' 3^5 lO oo ^ rtt CO I I ta. o C TJ ' O .-H P3 O T3 ;z: cS cS B tea 0) Q g 2 T3 13 ce t>j o > &H pH 'o >> ’xi ’ c -c 2 o 'S o rS ? «.s E ; expt. g plates ogen 0 -chemisl ting )ing nts ions rosin thylated SrS ^ O fH “J O 3 §D-i^ ^ ^ "Z p « 8 Ph H § ^ ’g ^ 2 P V S © pq p^ fiq pq pq pd pil P3^ p^ 148 ' CYCLOPAEDIC INDEX. T3 S "o O <1 o CO 2 .ph‘ O . j CO . g . . Oi — - ^ cq O O ta ■ 0+0 t, X^^vo ^ o PH ^ pc. * K o o o . M (J, Wg oR p o - lO 00 o'' ?o ^ O CO ^ Q ^ o -5 3 >, : O rQ P- Pa o o| §=£ o S _ 9 "o O P 3 ^ - 7 ; .p fl .:. +3 eg +0 O H P— I ca *rS -1 Oi CO CO (M ^ 2 CO CO I-H CO Oi ^ CO o -H CO “ 3 2 3 3 o s B qp B B O 5 oo >> T} s ■ “ • O a o ts fc: «> B ''3 CD cS ^ C c M o .2 2 -S ‘ '-*:. o ^ 0 rrt o p p P ^ P^ BT;'B'T3i2'^'^'^lllhr( WpqKWffiffiWW WKffi rB CB w w Sollibility in 100 Parts of 150 CYCLOPAEDIC INDEX. o o si o> CO o « J:; « !>• i-^ O • CO *■ ^ S •S 1 a . S 114 32 7, 9 75 130 11 7, 8 122 84,’l05 . t>. 00 nn O r-i CO CO rH CO CO .. rH l-H OO j CO 1 r— 1 tS3 % • . ® W). 'II c5 CN ?o ' Q^goio tH 1—1 s s ■s| , « 00 S OS rH CO *” (M r-H rH Cl w q W w" o o Mrf«8 w -H O es ;::5 fl o S -P Q)P-I 00 ” tCo'*'® CO 1-1 OO <© )0 _ 1 . O rH ; Il< Tt< I-H 2 «o (N • a •rt p .s ^ r— O ^ • ba d CO "d o a> .d ^ ^ t^ ’« ‘x ooo m d Ps ^ g _ 1i C3 S5?S »• o ?D § CO CN g CO ^ CO Tf Oi 05 05 ;^OOC5g 05 05 g05 CO 'r^^ ^«05 >> 0 w" • • 05 . • • §S'5.| ««g M 0 ® Ph eo M CO + CD >5 0 r® Pm la WO Om w 0 § <0 . .0 w 0 w^ •JO . . .0 M 1 0 S3 , -S cTD Jh ' .2 • -H 0 1 CQ OT c3 s s ! § rC 2 c£l ' OT ^ OT .. • ® ,0 6 ^ - ^ .2 -M ^ 0 CC 2 S, 1 (=4^:3 PM P 3 § 1 ® o3 ® 1 >H 0 .0 I’fe p ? 1C5 1-H 05 « ^O 05 CO lO 1-1 »-i CO S 05" 05 j>. 05 O oT J>. 05 CO CO iO 00 05 -rtT 05 05 «o i>r iO r2 .S '"S -2 § o |:§ .1^ o o 5 M f-. c3 >, -2 oqo ® ® ® * ••-1 rP ce 3 3 3 cS 3 c 3 ® OT g (>5 0 P 33 ? 2 3 fco ^3 3 Pm s Pm W 3 .S g'S 2 2 3 >> PhPwPh P5 fcc .S 2 -a o o ^ g O “ T; CO OT (D O 0^ Sn “ ,£ 01 g O ^ T-l Co" C o PhPh C3 M m g rQ O C3 (D io'-^ p p o P rP S -t^PrP^C3M(rO-^g ^ — * C^I— ' 05*^ ^ ^ ><1PPPP o> o) m3 :gh CO maiai ^ 3 ••4 ^ ••4 .4; ..4 .,4 ot> 5 c5 6 oo QJ CD 1 -H ^ 00 00 ^ lO OO 00 (M ^ (M (M t-h so CT (M lO 00 ^ CO (M Ttt -CM o' bc o^ >-* g W 2 S cT + 20 0^03 ^ 3 M cT 15 O) . O M “ “ O o ^ 01 1^11 ^ S 3 3 O cS 03 • ’4j3^CO00C02^^rHCO'cti ooCO <^00 ~ CO CO •t-H 0 CD 01 — ■ CO CO 'Cf O O OO* C> w (D o) 3 'ri ■Ti -t^ 43 >-0 o o \ 9^4= 'B ’'Or^ P-( 34 oK Wffi W IS d 3 VI o 'B ^ K H 156 CYCLOPEDIC INDEX. 6 J bD . •S II .00^»i:5 • ' • S • d • .2 O gl § a 3. § -^ „r • El d 3 g -fH M rd rd 2 2 o :d f-i cc W i 03 ' ]'§,' T3 ' o : CYCLOPAEDIC INDEX. 157 o CO . (M O ^ . T— I Cq I— I rH CO CO CO rH GO 00 o CO 00 oo r-Ht^OOOOOOOOOiOi ocococococococo t-H i-H I— I rH »-H T— I t-H . O U5 01 S CO CM r-l ^ rl.CM CO c» S’ ^ ._r Vh (N CO 05 -rji r— H 05 ^ rH C5 C O ^ ^ O t-| Q. 05 05 05 -)-3 . -|J -M 4J c3 ^ cS ca ^ r> s: 3 2"^ §OPQ ° NEILL AND COMPANY, PRINTERS, EDINBURGH. LIST OF BOOKS FOR Architects, Painters, P HAND-BOOKS FOR WATCHMAKERS, k. SPONS’ MECHANICS’ OWN BOOK. Foreign Docks imported to order. American Agents for the Photogram, |i. lo per annum, and the Process PhotogTam, | 2 .oo per annum. Subscriptions received for all American and Foreign Technical Journals. We shall be pleased to mail any book post-paid to any address i in the world, on receipt of published price. (2;^"Send full postal address. Amounts for less than $i.oo can be sent in U. S. Postal Stamps. Remittances should be made either by P.O.O., Express Order, I Registered letter or Draft, and made payable to SPON & CHAMBERLAIN, Publishers of Technical and Scientific Books, 1 2 CORTLANDT STREET, N EW YORK, U. S. A. Long Distance Telephone. i ^ namAL or in/truction IN-= H ARD S OLDERING. HARVEY ROWELL. CONTENTS. Introduction. Utensils and Chemicals. — The flame. Lamp. Charcoal. Mats. Blowpipes. Wash-boitle. Binding wire. Borax. Chemicals. Alloys for Hard Soldering. — spelter. Silver solder. Gold solder. Oxidation. — Oxidation of metals. Fluxes. Anti-oxidizers. Structure of Flame. — Oxidation of gases. The cone. Oxidizing flame. Reducing flame. H^^at. — Transmission. Conduction. Capacity of metals. Radiation. Application. The Process. — The work table. The joint. Applying solder. Apply- ing heat. The use of the blowpipe. Making a ferrule. Joints. To repair a spoon. Difficulties. To repair a watch case. Hard soldering with a forge or hearth. Hard soldering with tongs. • Technical Notes. — Preserving thin edges. Silversmiths’ pickle. Re- storing color to gold. Chromic acid. Steel springs to mend. Sweating metals together. Retaining work in position. Making joints. Applying heat. Preventing the loss of heat. Effect of sulphur, lead and zinc. To preserve precious stones. Annealing and hardening. Burnt iron. To hard solder after soft solder. Properties of Metals. — Tables of specific gravity. Table of tenacity. Table of fusibility. Fusibility of alloys. 56 Pages, 12mo, Cloth, Price, 75 Cents. 2 Now rmdy. Containing 702 pages, Svo, cloth, with 1420 illustraMons. SPONS* MECHANICS’ OWN BOON. A MANUAL FOR HANDICEAFTSMEN AND AMATEUKS. The title of this work almost suffices to indicate the character of the contents. The various mechanical trades that deal with the conversion of wood, metals, and stone into useful objects are explained from an every day practical view. The method of treatment of each branch is scientific yet simple. First in order comes the raw material worked upon, its characters, vari- ations, and suitability. Then the tools used in working up the material are examined as to the principles on which their shape and manipula- tion are based, including the means adopted for keeping them in order, by grinding, tempering, filing, setting, handling, and cleaning. A third section, where necessary, is devoted to explaining and illustrating typical examples of the work to be executed in the particular material under notice. Thus the book forms a complete guide to all the ordinary mechanical operations ; and whilst professional workmen will find in it many suggestions as to the direction in which improvements should be aimed at, amateur readers will be glad to avail themselves of the simple directions and ingenious devices by which they can in a great degree overcome the disadvantage of a lack of manipulative skill. Price $2.50 postpaid. 3 2 S PONS’ MECHANICS’ OWN BOOK. CONTENTS. Mechanical Drawing: buying and keeping instruments; draw- ing boards; scales; squares; paper; mounting; mounting on linen; pencil- ling; erasing errors; inking; testing straight-edge; using parallel rules; using compasses; tints, dimensions, and centre lines; title; nature of drawings; finishing a drawing, colours; shading; colouring tracings; re^ moving drawings from the board; mounting engravings; fixing pencil drawings; tracing-paper; transfer-paper; copying drawings pages 1-13 Casting’ and Founding : general outline of the operations. Brass and Bronze Casting: characters of the various alloys employed, reactions of the metals on each other, mixing the metals, effects of tempering; fur- naces, their construction, means of producing draught, fuel, the ordinary cupola, the ordinary melting furnace, the circular melting furnace, the reverberatory furnace; crucibles; moulding; facing the moulds, filling the moulds, moulding in wax, /onnu perdrdu method, castings of natural ob- jects; casting, pouring the metal, temperature for pouring, escape of gases from the mould, ornaments in relief; cores; making bronze figures; using plaster patterns, finishing the casting; bronzing its surface, Japanese bronzes, inlajung on bronzes: casting en cire perdue, the model, reproduction in wax, formation of the core, constructing the lanthorn, re- touching the wax bust, preparing the bust before making the cope, for- mation of the cope, firing the block, the final casting in bronze. Iron Founding: pattern-making, cores, shrinkage, taper; tools, crucibles, pots, moulding flasks, packing the flasks, clamping them; casting in sand, with and without cores, casting in loam, forms of castings; examining castings as to quality and soundness; shrinkage of iron castings; chilling iron castings. .. 13-44 Forging’ and Finishing : definition of the terms; explanation of the technical phrases, to make up a stock, fireirons, rod, bar, plate, to take a heat, to finish at one heat, to draw down, to draw away, to upset, scarf- ing, butt-weld, tongue-joint, to punch, to drift out, the hammerman, the tuyere or tweer; forges or liearths; anvils; vices and tongs; hammers; cut- ting tools, principles and practices in making chisels; drilling and boring, construction of drills; swaging tools; surfacing tools, fillingup, cleaning clogged files, polishing; screw cutting tools; forging: welding, wrought iron, steel to wrought iron; tempering, hardening, softening, annealing, the colour scale, case-hardening; examples of smiths’ work, — making keys, bolts, nuts, tongs, hammers, chisels, files, scrapers, di-ifts, punches, spinners, wrenches; red-lead joints; rust joints; riveting .. .. 44-90 Soldering’ : solders, composition and chai-acters of these alloys; colouring solders to match metals. Burning or Autogenous soldering: adaptations of the process, application to pewter, brass castings, iron castings, stove plate; burning seams in lead; the burning machine, air- vessels, bellows, tubes, jets, wind guards. Cold soldering: the flux, the solder, application. Hard soldering various metals and objects. Soft soldering: the solders, fluxes, irons, and bits employed, and precautions 4 SPONS’ MECHANICS’ OWN BOOK. 3 needed. Generalities, — including blowpipes, lami3s, mechanical blowers, supports, tools, braziers’ hearth, means of heating the iron; hints on fluxes, spelter, commercial grades of solder, cleaning impure solder, soldering zinc and galvanized iron, soldering without an iron, soldering- brass to platinum, soldering brass to steel, soldering iron and steel, soldering silver, soldering platinum and gold, mending tin saucepans, soldering pewters and comiio pipes, laying sheet lead, mending leaden pipe, blowpipe brazing .. .. .. .. .. .. .. 90-116 Sheet-metal working: Striking out the patterns. Tools, — mallet, cutting, flattening, folding, and forming tools. Working the metals , — seamless goods, bending, spinning; seamed goods, pipes, cups, square boxes, riveting 116-126 Carpentry ; ITbods; acacia, alder, apple, ash, beeches, birches, blackwood, boxes, cedars, cedar boom, cheny, chestnut, cyjiress, cypress pine, dark yellow-wood, deal, dogwoods, ebony, elms, eucalyiitus, fir, greenhart, gums, hickories, ironbark, ironwood, larches, lignum-vitas, locust-tree, mahoganies, mango, maple, muskwood, oaks, pear, persim- mon, pines, plane, poplar, rosewood, satinwood, she-pine, sneezewood, spruces, stringy-bark, sycamore, Tasmanian myrtle, teak, tulip, walniits, willow, yellow -wood, yew; British Guiana woods; Cape, Natal, and Trans- vaal woods; Ceylon woods; English woods; Indian woods; New Zealand woods, Queensland woods; Straits Settlements woods; Tasmanian woods; West Indian woods; growth of wood; felling; squaring; defects; selecting; classification; market forms; seasoning; decay; preserving; fireproofing; shrinkage; composition; strength; measuring. Tools: Guiding tools, — chalk line, rule, straight-edge, squares, levels, bevels, mitre-box, com- passes, callipers, shooting-board; Holding tools, — pincers, vices, clamps; Rasping tools, — saws (principles, qualities, selecting, using, filing, setting, sharpening, gumming; examples of teeth for cross-cuts, back-saws, buck- saws, rip-saws, circular saws, band-saws, jig-saws, table for jig and cir- cular saws, home-made fret-saw); files; Edge-tools, — chisels and gouges, spokeshaves, x^lanes, sliaiqiening methods (grindstones, oilstones), mis- cellaneous forms (circular i^lane, rounder, box scraj)er, veneer scraper, mitre-plane, combination fibsters, adjustable dado); Boring tools, — awls, gimlets, augers, bits and braces, drills, (angular bit stock, countersink, expansion bit, boring machine) ; Striking tools, — hammers, mallets; Chop- ping tools, — axes and hatches, adzes; Accessories, —bench, bench-sto] 3 s, holdfasts, sawing rest, bench-vices; nails, nail-iDuncli, nail-jiuller; screws, screw-driver. Care of Tools: wooden parts, iron parts, rust j^reventives, rust removers. Construction: joints, princqiles of joints, equal bearing, close jointing, strains, classification of fastenings, lengthening joints, strengthening joints, bearing joints, jiost and beam joints, strut joints, miscellaneous joints, keying, corner-ijiecing, mortising and tenoning, half-lap joint, dovetailing, blind dovetails, mechanical aids in dovetailing, do welling, joining thin woods, glueing, hinging. Examples of Construction: workshoji ai'»j)liances, — tool-chest, caipenters’ bench, grindstone mount; rough furniture,— steals, ladders, cask-cradle, tables, seats (box stool, 3-legged stool, chairs), washstand, bedstead, chest of drawers, dresser, garden and yard accessories, — wheelbarrow, jioultry and jiigeon houses: hives, forcing frames, greenhouses, summerhouses, fences, gates; house building, — floors, roofs, doors, windows 126-350 Cabinet-Making-: Woods: apjile, ash, beech, beefwood, birch, box, canqihor, canary, cedar, cherry, ebony, holly, lime, locust-wood. 4 SPONS’ MECHANICS’ OWN BOOK. mahogany, maple, oak, partridge-wood, pear, pine, plane, rose, sandal, satin, teak, tulip, walnut, zebra. Tools: tool-chest, bench, planes, sawing rest, moulding board, mitring and shooting board. Veneering: cutting veneers, fixing the veneer; inlaying, imitation inlaying. Examples: couch, chairs, folding bookcase, chest of drawers, wardrobe, sideboard 350-386 Carving and FreWork : Carving: woods, — camphor, ebony, lime, mahogany, oak, pear, sandal, sycamore, walnut, wild cherry, yew; qualities of wood, staining, adaptability; tools. Fretwork: woods; tools 386-399 XTpliolstery ; tools; leather work, — small chair buttoned and welted, easy chairs, settees and couches; hair cloth; fancy coverings, — plain seats, buttoned seats, spring edges, needlework chairs; mattresses, — spring, tufted top, folding, stuffed; beds and pillows 399-405 Painting, Graining, and Marbling : Painting: definition of paints; basic pigments, — white-lead, red-lead, zinc oxide, iron oxide; colouring pigments,— blacks, blues, browns, greens, lakes, oranges, reds, yellows; mediums, — linseed-oil; driers; grinding; storing; priming; filling, coats; brushes; surface; removing old paint; cleaning paint; knotting; water-colours; discoloration; miscellaneous paints, — cement paint for car- ton-pierre, copper paint, fioor painting, gold paint, iron paint, lead paints, lime paints, silicated paint, tin-roofing paint, transparent paint, window paint, zinc painting; composition of paints; measuring painters’ work; painters’ cream ; wall painting, frescoes, spirit fresco, preparing the ground, the pigments admissible for colouring, preparation of the colours, produc- tion of delicate tints, the fixing medium. Graining: colours, tools; styles of graining — ash, chestnut, mahogany, maple, oak (light and dark), rose- wood, satinwood, walnut; hints. Marbling: the production of painted surfaces in imitation of black and gold, black Bardilla, Derbyshire spar, dove, Egyptian green, granites, Italian jasper, royal red, St Ann’s, sienna, and verd antique marbles .. - 405-433 Staining : objects to be attained, essential features to be observed; recipes for black stains, black-board washes, blue -stains, brown stains, ebonizing, floor staining, green stains, gray stains, imitating and darken- ing mahogany, oak stains, purple stains, red stains, imitating satinwood, violet stains, imitating and darkening walnut, and yellow stains 433-446 Gilding: the process; leaf metals; composition and characters of the sizes used for attaching the leaf; tools and apparatus. The operation of Dead gilding, — preparing the surface, transferring the leaf to the surface, when to lay it, making good the blank spaces, completing the adhesion, sizing the surface; modifications for dead gilding on plain wood, polished wood, cards, textiles, painted and japanned surfaces, metals, masonry, ivory, and plaster of Paris. Bright Gilding — on transparent and opaque material, securing adhesion of the leaf, making fancy patterns 446-449 Polishing: principles. Marble polishing: producing a plane sur- face, taking oft’ the rough, polishing up, rendering brilliant, filling flaws; polishing imitation marbles. Metal polishing: polishing metallic surfaces by hand, best means of conducting the operation, running work in the lathe, relative merits of oils and water; Belgian burnishing powder; brass- polishes; burnishing, kinds of burnishers, precautions in using the burn- isher; variations in the tools and methods adapted for plated goods, gold and silver leaf on wood, gold leaf on metal; leather gilding; engravers’ burnishers; clockmakers’ iDurnishers; burnishing book e%es, cutlery, pew- ter, and silver; making crocus; emery paper, emery paper pulp, emery wheels; friction polish; german silver polish; glaze wheels for finishing 6 St»ONS’ MECHANICS’ OWN BOOK. Bteel; polishing gold and silver lace; polishing and burnishing iron and steel; plate powders: prepared chalk; putty powder; razor pastes; rotten- stone or tripoli; rouges. Wood polishing: what it consists in, the prelim- inary filling in, smoothing the surface, rubbing in linseed-oil, the founda- tion coat of polish, the bodying-in process, allowing to harden, putting on the final polish, original recipe for making the finishing polish; general method of wood polishing adopted in America; the processes carried on in first-class piano factories; collection of recipes for furniture creams, French polishes, reviving fluids, compounds for darkening furniture, wood-fillers, and mixtures for black woodwork, carvings, antique furniture, fancy woods, black and gold work, white and gold work, etc. ; polishing woods in the lathe, modifications to suit hard and soft woods M9-472 Varnishing’ ; nature of varnishes, points governing their qualities, ingredients of varnishes; the principal resins and gums, their varnish- making qualifications; solvents and their suitability; driers and the ob- jections to them; kinds of varnish and their essential differences; mixing varnishes, white oil varnishes or spirit and turpentine varnishes; rules regulating the application of varnishes; recipes for compounding oil var- nishes (copal, amber, Coburg, wainscot, etc.), turpentine varnishes, Brunswick black, and varnish for ironwork 472-475 Mechanical Movements : simple, compound, and perpetual mo- tion; pulleys, blocks and tackle, mangle-wheel and pinion, fusee-chain and spring-box, frictional clutch-box, throwing in and out of gear the speed motion in lathes, tilt-hammer motion, ore-stamper motion, reciprocating rotary motion, continuous rotary motion converted into intermittent rotary motion, self-reversing motion, eccentrics, crank motions, cams, irregular vibrating motion, feed-motion of drilling machine, quick return crank motion of shaping machines, rectilinear motion of horizontal bar, screw bolt and nut, uniform reciprocating rectilinear motion, screw stamping press, screw-cutting and slide-lathe motion, spooling-frame motion, micro- meter screw, Persian drill, rack and pinion, cam between friction rollers in a yoke, double rack, substitute for crank, doubling length of stroke of piston-rod, feed-motion of planing machines, fiddle drill, bell-crank lever, motion used in air-pumps, shears for cutting met,al plates, lazy tongs, toothed sectors, drum, triangular eccentric, cam and rod, expansion eccentric, rack and frame, band-saw, toggle-joint for punching machine, silk spooling motion, yoke-bar, steam-engine governor, valve motion, ellipsograph, elbow-lever, pawl and elbow-lever, treadle and disc, water- wheel governor, knee-lever; spiral grooved drum; valve motion and revers- ing gear, obtaining egg-shaped elliptical motion, carpenters’ bench clamp, uncoupling engines, varying speed of slide in shaping machines, reversing gear for single engine, diagonal catch and hand-gear, disengaging eccen- tric-rod, driving feed-rolls, mangle-wheel and pinions, mangle-rack, roll- ing contact, wheel and pinion, ratchet-wheel, worm-wheel, pin-wheel and slotted pinion, Geneva stop, stopsj for watches, cog-wheels, roller motion in wool combing machines, drag-link motion, expanding pulley, chain and chain pulley, lantern-wheel stops, tappet-arm and ratchet- wheel, spur-gear stops, brake for cranes, dynamometer, pantograph, union coupling, anti-friction bearing, releasing sounding-weight, releasing hook in pile-giving, centrifugal check-hooks, differential movement, combina- tion movement, series of changes of velocity and direction, variable motion, circular into reciprocating motion, Colt’s revolver movement, Otis’s safety stop, Clayton’s sliding journal box, Pickering’s governor, windlass, rack 7 SPONS' MECHANICS’ OWN BOOK. and pinion for small air-pumps, feeding sawing macbine, movable head of turning lathe, toe and lifter, conical pendulum, mercurial compensation pendulum, maintaining power in going barrel, parallel rulers^ Cartwright’s parallel motion, piston-rods, gyroscope, gyroscope governor, drilling apparatus, see-saws, spiral line on cylinder, cycloidal surfaces, polishing mirrors, edge-runners, portable cramp drills, tread-wheels, pendulum saws, adjustable stand for mirrors, cloth-dressing machine, folding ladder, lifting jack, jig-saw, polishing lenses, four-way cock, continuous circular into intermittent rectilinear reciprocating motion, repairing chains, Wilson’s 4-motion feed for sewing-machines, describing parabolas, cyclo- graphs, describing pointed arches, centrolinead, proportional compasses, Buchanan and Kighter’s slide-valve motion, trunk-engine, oscillating pis- ton engine, Boot’s double quadrant engine, rotary engines, bisecting gauge, self-recording level, assisting crank of treadle motion over dead centres, continuous circular into rocking motion. Boot’s reciprocating en- gine, Jonval turbine, reciprocating motion from continuous fall of water, water-wheels, Fourneyron turbine. Barker mill, tumbler, water-raising machines, Montgolfier's hydraulic ram, swing boat, lift-pump, force- pump, rotary pumps. Hero’s fountain, counter-balance bucket, pulley and bucket, reciprocating lift, Lansdell’s steam siphon pump, swinging gutters, chain pumps, steam hammer, Hotchkiss’s atmospheric hammer, rotary motion from different temperatures in two bodies of water, flexible water main, air-pump, aeolipile or Hero’s steam toy, Brear’s bilge ejector, gasometer, common windmill, vertical windmill, paddle-wheel, screw pro- peller, Brown and Level’s boat detaching-hook, steering apparatus, capstan, tongs for lifting stones, fan blower, siphon pressure guage, mercurial barometer, epicyclic trains, aneroid or Bourdon gauge; gearings, brush wheels, friction wheels, sun-and-planet motion, mangle or star wheel, jumping rotary motion, registering revolutions, mangle-rack, wheel-work in base of capstan . . 475-531 Turning- : the operation. Lathes, mandrels, chucks, poppet-heads, rests, supports, boring collars, true frames, self-acting slide-rest, complete double-gear foot-lathe, single-gear foot-lathe, compound slide-rests; form of tools, shape of cutting edges, angle of holding, screw cutting, skilful- ness with hand tools. Tools: their selection. Metal-turning tools : their temper, grinding, cutting angles; iron -turning tools: common roughing tool, round nose, parting tool, knife tool for finishing edges and faces, boring tools for hollow cylinders, square nose, scraping tool, spring tool, finishing tools for rounded work; brass-turning tools; adapting tools; making a grindstone; whetting tools; making milling tools for screw-heads; making centre punches and drills; scribing block. Tool-holders: the swivel tool-holder and its adaptation to various needs — e.g. planing under horizontal surface of a lathe-bed, planing in a limited space, clearing a projecting boss, cutting a vertical slot, undercutting slots and clearance corners, cutting square threads; grinding the cutting edges, angle-gauges for maintaining correct forms; rehardening cutters. Drilling and boring tools; experiments on the cutting angle; why common drills run; the grinding line; grinding machines for twist drills. Milling: range of mil- ling machines; modern milling cutters — how they are made and set; vari- ous forms, —disc, cylindrical, circular saw-like, conical, annular, and complex forms; cutting speed and power required. Wood-turning tools; plain gouges and chisels; turning straight stuff; holding the tool; flaws in tools; selection of gouges and chisels .. .. , .. 531-561 S SPONS’ MECHANICS’ OWN BOOK. 7 Masonry \ Stoneioork: durability of natural stone, physical struct- ure and its influence; working; hardness; strength; weight; appearance; position in quarry; seasoning; natural beds; destructive agents, — chemical, mechanical, lichens, molluscs; quarrying;; granite; serpentine; sandstones; limestones; — marble, compact limestones, shelly limestones, magnesian limestones, preserving, — painting, silicatising, other processes; stone- masons’ tools, — saws, mallets, chisels; laying stonework, — rough rubble, course rubble, combined rubbles, ashlar work; joining stones; stone walls. Brickwork: bricks,— classification, cutters, rubbers, ordinary building, underburnt; qualities of a good building brick; size; testing. Terracotta blocks, joining them, their advantages and disadvantages. Limes: rich or fat limes, poor limes, hydraulic limes. Sand: argillaceous, siliceous, and calcareous, its characters and impurities; washing, substitutes. Mortar: its quality governed by that of its constituents; danger of using fat limes; superiority of hydraulic lime and cement; objects of using sand, and con- ditions to be observed; choice of water; proportions of sand desirable; measuring the ingredients of mortar; mixing the mortar; selenitic mor- tar; lime and cement mixtures; grout; moisture essential to the setting of mortars. Bricklayers’ tools. Laying bricks: sizes, breaking joint, bond; headers, stretchers, and closers; English and Flemish bond; raking courses in thick walls; keeping the work level and plumb; ensuring adhesion between the brick and the mortar; pointing and finishing brickwork, — striking,, tuck pointing, weather joint, bastard tuck, bastard-tuck pointing, evils and uselessness of the common methods and description of how it should be done; examples of first and second course of walls in various styles of bond; hollow walls; fireplaces. Concrete: the materials compos- ing it, their choice and proportions; mixing; laying moulds for construct- ing walls; the cementing material; bulk produced; selenitic concrete; expansion of concrete. Saltpetreing of walls — causes and cure. Damp walls and their prevention. Scaffolding for bricklayers . . 561-604 Plastering* and Whitewashing’ : Plastering: materials, — basis of plasters, Portland cement, Parian or Keating’s cement, composition of the several coats; lime, water, and hair used; coarse stuff,' fine stuff, plas- terers’ putty, gauged stuff; selenitic plaster; rough cast; stucco; Marezzo marble; mouldings and ornaments in plaster and papier mache; tools; lathing; laying and pricking-up. Whitewashing, Calcimining or Distemper Painting: common whitewash or lime whiting; common colouring, making whiting; white and coloured distemper; indoor operations on good ceilings; a simple lime-wash ; a good stone-colour wash ; a waterproof calcimine that bears washing; re -whiting an old dirty ceiling; further hints and recipes for milk distempers and whitewashes 604-613 Roofing : pitches of roofs; thatching; shingles or shides; felt; Willes- den paper; slates; tiles; metallic roofing .. .. .. .. 613-627 Glazing: Glass of various kinds; putty, to soften putty; tools; lead glazing; special methods of glazing not dependent on putty 627-634 Bell-hanging : the ordinary domestic bell system, tubes, wires, cranks, gimlet, bells, and general directions; electric bells, — the battery, wires, circuit-closer, bells, arrangement of series; systems with 1 bell and 1 press button, 1 bell and 2 buttons, 2 bells and 1 button, annunciator system, double system, bell and telephone; making electric bell, — back- board and cover, electro-magnet, bobbins or coils, filling the bobbins with wire, putting the bell together 634-640 Gas-fitting : fixing brackets and pendants, using the tongs 640-642 9 SPONS’ MECHANICS’ OWN BOOK. Paper-hanging : classification of wall papers, their characters and uses; colours to avoid; papers for damp walls; varnishing, sizing, painting and washing wall papers; wall papers considered as ornament, and rules as to colour, pattern, dado, and frieze; pasting, cutting, and hanging the paper, and precautions to be observed .. .. .. .. 642-646 Lighting : natural lighting, window area; artificial lighting by can- dles, oils, gas, and electricity. Oil lamps, their principles, and the objects aimed at in the various forms -of wick, burner, and regulator. Gas, how supplied, computing the number of burners necessary, advantage of a ventilator; how to turn off gas at night; construction of burners and con- ditions that govern it; distribution of jets; selection of glass globes; how to utilize fully the luminosity of the gas. Electric lighting, — rules and regulations for minimizing risk, joining the wires .. .. '646-654 Ventilating : window ventilators, Butler’s system, Arnott’s system, Morse’s system, American plan in large buildings, method at St. Thomas’s Hospital, method at Guy’s Hospital, Harding’s ventilators, system adopted by the Sanitary Engineering and Ventilating Co., Boyle’s air-pump venti- lators, Kershaw’s chimney cowl 654-658 "Warming: conserving heat, double windows; radiant heat and hot air, their relative position as regards health; open grates; open stoves, economizing fuel with ordinary grates; close stoves; hot-air furnaces; hot- water heating; steam heating 658-667 Foundations : points to be considered ; foundations on rock, gravel, sand, clay, firm ground overlying soft ground, soft ground of indefinite thickness; concrete; fascines; piling; footings; damp course .. 667-670 Roads and Bridges : Boads: the original foot tract, temporary roads in unmapped country, one made across the Chenab; plank roads and turnouts; pavements, — flagging, asphalt, ^cement floors. Bridges: simple timber bridge, paved causeway, boat bridges, travelling cradles, rope bridges, weighted beams 670-676 Banks, Hedges, Ditches, and Drains 676-677 Water Supply and Sanitation: river water, cleansing; spring water, filtering; wells, sinking in various strata, steining, simple plan used in India; pumps and various other methods of raising water; ponds, cavern tanks, artificial rain ponds. Drains and traps 677-680 House Construction : Log huts, building the fireplace. Frame houses. Earth walls. Stairs. Colonial houses, — peculiar conditions of build- ing in Canada, Ceylon, and India, to suit the climatic requirements 680-688 SPON & CHAMBERLAIN, PUBLISHERS, IMPORTERS AND BOOKSELLERS, )2 CORTLANDT STREET, NEW YORK. 10 2g PLATBS, 5 K in. X 8 in. PRICE 50 CEXTSe A SYSTEM OF EASY LETTERING. BY J. HOWARD CROMWELL. ATJTHOB OF “A TEEATISE ON TOOTHED GEABING,” "A TKEATISE ON BKI.TS AND PULIiETS.” This useful -work gives twenty-six different forms of alphabets, all constructed on the same general system. The space to be lettered is to be divided into parallelograms or squares, as the case may be, and within these as a guide the different letters are drawn and inked. The guide squares, which have been made in pencil, are then erased, leaving the final letters. On so simple a basis as this quite a variety of effects are produced in flat and block letters. Scientific American. This little book will be appreciated by draftsmen who wish to use plain letters (and yet somewhat different from the ordinary run of letters) for the titles on drawings. The book vdll also be valuable and useful to any one who has had no practice in lettering, as the easy method given for forming the letters will enable a person to form the letters correctly, and with a little practice to do so quickly. Amen'ican Machinist. Mr. Cromwell has done a good work in getting out this little book, providing a system of lettering which is both neat and easy of execution. Instead of giving the conventional series of ornamental letters, many of which take more time than the drawing is worth, we have here several alphabets which give sufficient variety for all ordinary purposes, and yet are so simple as to be within the range of ability of the freshest ap- prentice. "We recommend the book to every draftsman. Mechanics. After forty years experience in mechanical and architectural drawing in this and other countries, we consider this among the best, most practical and useful books that treat on lettering for ordinary" practical purposes. Master Steam Fitter. Designs are given in great variety, and the lines of projection given with them enables any one to enlarge or reduce with great ease and exact- ness. Manufacturers Gazette. II 12 Books for Architects. Hngflisll Arcliitecture,— The Seven Periods of English Architecture, defined and illustrated. By Edmund Sharpe, M.A. Contents of Chapters ; i. — Introduction. 2. — Classification. 3. — Compartments. 4. — Saxon Period. 5. —Norman Period. 6. — Transi- tional Period. 7. — Lancet Period. 8. — Geometrical Period. 9. — Curvilinear Period. 10. — Rectilinear Period. With 20 full-page steel engravings and wood cuts. 8vo., cloth. $5.00. Plan and Map Drawing:.— The Draughtman’s Handbook of Plan and Map Drawing. Including Instructions for the Prepara- tion of Engineering, Architectutal and Mechanical Drawing. By Geo. Andre, C.E. Contents. — Part i. — T he Essential Elements. The Drawing Office and its Furnishings. Geometrical Problems. Lines, Dots and their Combinations. Colors. Shadings Part 2. Applications, Lettering, Bordering and North Points. Scales. Plot- ting. Civil Engineers and Surveyors’ Plans. Regulations of Local Government Board. Map Drawing. Mechanical and Architectural Drawings. Copying and Reducing. Trigonometrical Formulae. Inclined Measure. Curvature and Refraction. Index. 150 pages. 86 illustrations, numerous tables and 33 plain and colored plates. -|to., cloth. $3-75. Scamping 'Trick.S, and Odd Knowledge Occasionally Prac- tised upon Public Works. Chronicled from the Confessions of some old Practitioners. By John Newman. Contents : i. — Introduc- tion. 2. — Screw Piles — General Consideration — Manipulation for “Extra Profit.*’ — Screw Piles — Details. 4. — Iron Piles— Arrange- ment Driving — Sinking by Water-Jet. 5. — Timber Piles. Pile-driv- ing— General Considerations. 6. — Timber Piles — Manipulation for “ Extra Profit.” 7. — Masonry Bridges . 8. — Tunnels. 9. — Cyl- inder Bridge Piers. 10. — Drain Pipes — Blasting and Powder- carriage. II. — Concrete-Puddle. 12. — Brickwork — Tidal Warn- ings — Pipe Joints— Dredging. 13. — Permanent Way. 14. — “Extra” Measurements — Toad-stool Contractors — Testimonials. 15 — Men and Wages — “ Sub,” from the word — A Subcontractor’s Scout and Free Traveller. 129 pages, i2mo., cloth. $1.00* Drauglitsmaiisliip.— Hints on Architectural Draughtsman- ship. By G. W. Tuxford Hallatt. Contents Introduction. Freehand Drawing. Plans, Elevations and Sections. Perspectives, Etchings. Water-color Perspestives. Competition Drawings. Ar- chitecture and Good Drawing Inseparable. Concluding Hints. 80 pages, i6mo., cloth. 60 cts. Xlie Builder’s Clerk.. — A Guide to the Management of a Builder’s Business. By T. Bales. 92 pages, lomo., cloth. 60 cts. Xlie Clerk of Works. — A Vade Mecum for all Engaged in the Superintendence of Building Operations. By G. G. Hopkins. 53 pages, i6mo., cloth. do cts 13 Architectural Examnles BRICK, STONE, WOOD AND IRON. BY WIZZIAM FXILLEItTON, Architect. A complete work on the Details and Arrangement of Building Construction and Design. Containing 200 plates with numerous drawings selected from the Architecture of former and present times. The details and designs are drawn to scale %-inch, J^-inch, y^-mch, and full size being chiefly used. The plates are arranged in two parts. The first part contains details of work in the four principal building ma- terials, the following being a few of the subjects in this part : Various forms of doors and windows, wood and iron roofs, half-timber work, porches, towers, spires, belfries, flying buttresses, groining, carving, church fittings, construc- tive and ornamental iron work, classic and gothic molds and ornament, folia- tion (natural and conventional), staiiied glass, colored decoration, a section to scale of the Great Pyramid, Grecian and Roman work. Continental and English Gothic, pile foundations, chimney shafts according to the regulations of the London County Council, Board schools. The second part consists of drawings of plans and elevations of buildings, arranged under the following heads : Workmen’s cottages and dwellings, cot- tage residences and dwelling houses, shops, factories, warehouses, schools, churches and chapels, public buildings, hotels and taverns, and buildings of a general character."” - All the plates are with particulars of the work, with explan- atory notes and dimensions of the various parts. The purpose of this book is chiefly to serve as a condensed form of refer- ence for examples of the most essential parts of building construction and ornament, classified, but arranged somewhat in the nature of a sketch-book. The work is also intended to be of use to the student and those already actively engaged in architectural work, whether designing the arrangement, construction, and ornament of buildings, or engaged among the different trades in their execution. In Demy Do, handsomely hound in cloth, PRICE, $6.00. 14 SECOND EDITION— REVISED. STANDARD PRACTICAL PIOMBIHG. BEING ol Complete Encyclopcedia for Practical Plumbers and Guide for Architects, Builders, Gas-fitters, Hot Water Fitters, Ironmongers, Lead Burners, Sanitary Engineers, Zinc Worhers, etc. CONTENTS OF VOLUME Lead and its manipulation. Lead and lead mines. Lead, separa- tion of silver from. Lead, red and white. Lead, use, nature, and properties of. Workshop and its tools. Lead casting and tools. Win dow lead. Lead barrel casting. Lead pipe. Lead pipe presses. Lead milling. Rolling-mills. Tin and its manipulation. l\letals and alloys. Solder. Sheet lead cutting. Soil pipes. Lead burning. Joint-making. Elbows and joints. Bends. Traps. Siphonage explained. Brass gratings. Cisterns. Filters. Sanitary plumbing job complete. Ven- tilation. Cowls. Wash-basins, baths, hot water supply. Proper house drainage. Joint-making. Testing drains. Soil and rain water pipe working. Tacks and ears. Astragals. Rain water pipes. Soil pipe and trap fixing. Waste pipe and trap fixing. Waste pipes and venti- lation. Closets. Urinals. Closet water supply. Closet valves. Closet service boxes and valves. Waste preventers. Lead light, and stained glass glazing. Ornamental lead light glazing. Stable drainage. 355 with 769 illii^trationi^. Small 4to, cloth, $3.00, 15 VOL. 2-NOW READY- PRACTICAL PLUMBING. BY PHILIP JOHN DAVIES. SYT^OfSIS OK COJ^TTEPiJXS. Introduction. Water Supply. — Wells, foul air in wells, well- heads, springs, percolation, artesian wells, well sinking, gas wells, well boring and artesian well tubes, well boring tools, windlasses and buckets, tube wells driving tube wells. Pumps. — Free pumps, hand, chain, bucket, jack, overhand, floating, wheel, hanging, plunger and lift pumps. Atmospheric pumps. Beer pumps Dia- phragm pumps. Bellows pumps. Fire engine and ships’ pumps. Repairing pumps, Pole and plunger pumps. Deep well pump work and rigging. Double and triple lift pumps. Working pumps. Horse driven pumps. Wind pumps. Puisometer pumps. Continuous “primed” pumps. Air chamber section pumps. Continuous action lift and plunger pump. Pump accessories. Garden pumps. Steam pumps, Turbines. Water motors. Hydraulic rams. Water pres- sure tables. Fountains, fitting up fountains. Hydraulic elevators. Pipe and joint tester. Water analysis. General town water supply. Table of the working strength of cast-iron pipes, weights and thick- nesses. Service pipes from street mains. Lead pipes. Bursting strain of lead pipes. Brass work, ferrules, stop ferrules. Tapping mmins. Tapping water mains under pressure. Tools and fittings. Analysis of tin, lead and plumber’s solder. Geometry for plumbers. (This article has been especially written for this work and is illus- trated with about 200 diagrams.) Mechanics for plumbers. Roof Work. —Lead laying. Gutters, drips and falls. Hints for measur- ing lead gutters. Dormers, welts and beads. Bossing up corners. Flats and seam rolls. Hips and ridges. Rain water pipes. Louvres and other ventilators. Turrets, spires, domes, skylights, lanterns, etc., etc. Stone channel gutters, stone coping or cornice gutters. Ornamental rain water heads. Finials and weather cocks. Solder dotting. Hot Water Baths, Heating, etc. — Sinks, lavatories, their fittings and accessories. Baths and bath fittings and accessories, Portable baths, hip baths, swimming baths. Repairing valves, cocks, etc. Bath distributors. Wash basins and fittings. Laundry drying rooms. Feed cisterns. Steam cooking ranges. Hydraulic press pipe joints. House heating by steam. Heating by hot water. Heating by radiators. Water boilers. Heating water by steam pipes (dry steam). Heating water by injectors (wet steam). Plumb- ers’ tools for iron pipe work. Stand pipes, fire plugs, tanks and cisterns. Water meters. Drinking fountains. Sizes of furnaces for heating different lengths of piping. Warmth and dust by hot water pipe heating. Hot water and steam thermometers. Heating ca- pacity. Jointing pipes. Examination questions. Complete index. 802 pages, 296 illustrations, 4to., cloth. $4.50.! 16 HOT WATER SUPPEY A PRACTICAL TREATISE UPON THE FITTING OF HOT WATER APPARATUS FOR DOMESTIC AND GENERAL PURPOSES. BY F. DYE. Contents. — Boilers. Cylinders and tanks. Pipes. Cocks. Circulation, explanation and cause. General description of apparatus. The high or old tank system. The cylinder system. Improved systems, etc. General directions, position of pipes, charging and testing, discolored water, etc. Experimental glass apparatus, results noted. Incrustation and causes, boiler cleaning, etc. Explosions and causes' -'safety valves, felting and jcacking pipes, etc. Coils and coil services, twin services, how to convert the tank system into tn.c cylinder s^’stem, how to lit a H.P. boiler to lie used for low pressure purposes at first. Estimates and estimating, (English). W orkmen’s tools. Common faults. The supply or ball-valve cistern, -pressure boilers. The subject is treated iu a very clear aud simple manner, and yet many points are brought forward which will be of service to skilled men. Boston Journal of Cor.i- rnerce. As boo water circulation is based upon certain definite scientific principles, the information contained in this book will be found valuable to those who are making a study of heating houses by hot water circulation, as well as those who are studying the means of domestic supply. American Artisan. The author Mr. Dye. has aimed to supply a book which is so plainly written tliat those who are unfaniiliar with the work may, without trouble, understand the methods which he explains. This done, it is perfectly certain that those who are familiar with the work by reason of their mechanical connection with it. will under- stand the reasons he gives for suggesting certain methods. The book seems the result of an intelligent aud earelul study of the subject, ana will be found exceedingly u.seful by all who have to deal with hot-water apxmratus. Building. Pipages, imth 25 illustrations, V2mo, cloth, $1.00 postpaid. 17 NEW EDITION, REVISED AND ENLARGED A PRACTICAL TREATISE UPON Wasming t 'Buildings BY HOT WATER, AND UPON Heat and Heating Appliances in general, with an inquiry respect- ing ventilation; the cause and action of draughts in chimneys or flues, and the laws relating to combustion. By CHAS. HOOD, F.R.S., F.R.A.S., &c. RE-WRITTEN BY FREDERICK DYE. OOITTEITTS- pl^EAT. Circulation of water. Air in pipes. Supply of water. Ex pansion of pipes. Irregular forms of apparatus. Causes affecting circulation of water and apparatus. Examples of hot water apparatus. Boilers. Boilers for brick setting. Appliances and fittings for horticultural works. Quantities for horticultural works. Fuel, stoking and attention to horticultural works. Upon warming buildings (low pressure). Pipes and appliances for building works. Quantities. Examples of low pressure apparatus for buildings. High pressure apparatus. Warming buildings by heated air. Hot-water works for baths, lavatories, and other domestic and general purposes. Combustion, its application to warming purposes by grates, etc. Chimneys. Ventilation. Appendix. Index. 512 PAGES, WITH 277 ILLUSTRATIONS, PRICE, $6.00. i8 T URKISH mTH. ITS DESIGN AND CONSTRUCTION. BY ROBERT OWEN ALLSOP. Contents. — Introduction. The general requirements of a public bath. The general disposition of plan of public baths. A detailed consideration of features peculiar to the bath. Heating and ventilation. Water-fittings and appliances. Lighting, decorating and furnishing. The Turkish bath in the house. The bath in public and private institutions. The Turkish bath for horses. Illustrated with twenty-seven plans and sections, from scale drawings by the author. 8VO, CLOTH, $2.50. TKe ril^DROi>AtHl( E5 TABli5HN|ENT flWO ITS BATHS, By ROBERT OWEN ALLSOP. Contents. — General considerations. Practical requirements of the Hydropathic establishment. Some existing institutions. Baths and treat- ments, and the arrangement of the bath house. Vapor baths and the Russian bath. The douche room and its appliances. Massage and electri- cal treatment. Pulverisation and the Mont Dore cure. Inhalation and the pine cure. The sun bath. Index. Illustrated with plans and sections. 8VO, CLOTH, $2.00. 19 CHARTS FOR Low Pressure Steam Heating FOR THE USE OF ENGINEERS, ARCHITECTS, CONTRACTORS AND STEAM FITTERS. By J, H. KIHEAI.Y, M.E. M. Am. Soc. M. A"., M. Am. Soc. of H. and V. Eng'rs., Ssfc. The author has long been in the habit of using charts to aid him in his work. Knowing the value of them in saving time, simplifying work and ensuring correct calculations he feels confident that they will be appreciated by engineers, architects and contractors, for whose benefit they have been compiled. Care has been taken to make the charts as clear and as easily understood and, above all, as accurate as possible. They have been based upon theoretical considerations, modified by what is considered to be good practice in this country. Chart i.— This chart is for determining the number of square feet of heating surface of a low pressure steam heating system, pressure not to exceed 5 lbs. per square inch by the gauge, necessary to supply the heat lost through the various kinds of wall surfaces of rooms. The chart is divided into four parts. Chart 2. — For deter- mining the diameters of the supply and return pipes for a heating system. Chart 3. — For finding the number of square feet of boiler heating surface and the number of square feet of grate surface for a boiler that is to supply steam to a steam heating system. Chart 4. — For determining the area of the cross section of a square flue, or the diameter of a round flue, leading from an indirect radiation heater to the register in a room to be heated. hull details are given for the use of these cards. These four charts are printed on heavy white card-board and bound together with cloth, size 13 in. by 9^4^ in., '[ hese cards are. securely packed for mail atid se?il to any part of the World on receipt of price. 20 Water Snpply, Plnmbing, Drainage, Hot 'Water Supply, A practical treatise upon the fitting of hot water apparatus for domestic and general purposes. By F. Dye. 82 pages, 25 illustrations, i2mo, cloth. $i 00. Hot Water Kittingf and Steam Cooking Apparatus. A guide for builders and others for the fitting and fixing of boilers and pipes for the circulation of hot water for heating buildings and for domestic purposes, with a chapter on boilers and fittings for steam cooking. By F. Dye. 92 pages, 23 illustrations, cloth, 50c. Plumbing:, Hraina^e and Water Supply, and Hot Water Fitting. By John Smeaton, C. E. Drainage. City wells. External plumbing. Internal plumbing and fittings. Tapping mains under pressure. Ornamental lead work. Heating. Hot water work, etc., etc. 236 pages, 217 illustrations, Svo., cloth. $3.00. Treatise on Modersi Sanitary Appliances for Healthy Residences and Public Institutions. By F. Colyer, C.E. For the use of students, etc. General instructions. Drainage. In- ternal work. Water supply. Heating apparatus for buildings. Swimming baths. Sundry sanitary arrangements in the construc- tion of residences, cleaning drains, etc. Electric light in residences and public institutions. Index, etc. 118 pages, i2mo., cloth, \ 2 00.* Bad Brains and How to Test them. With notes on the ven- tilation of sewers, drains, and sanitary fittings, and the origin and transmission of zymotic diseases. By R. Harris Reeves. 68 pages, 3 plates, i2mo., cloth. $1.40. Public Batbs and Wasbbouses. By Robt. Owen Allsop. Contents of Chapters ; — i. Introduction. 2. Schedule of accomodation. 3. General arrangement of baths and washhouses. 4. Slipper baths. 5. Swimming baths. 6. The public washhouse. 7. The establishment laundry. 8. The engineer's department, q Water supply. 10. The heating of swimming baths, ii. The Turkish bath in public bathing establishments. 12. Baths for the poor. Index. 98 pages, 18 illustrations and 4 folding plates, 8vo, cloth, $2.50. Hints to House Hunters and 'House Holders. By Ernest Turner. Chapter Headings : — Househunters and House- holders. 2. Requirements. 3. Situation and aspect. 4. Soil. 5. Con.struction. 6 Water supply. 7, Drains. 8. Ventilation and heating. 9. Warming and ventilation. 10. Light, ir. Dust. 12. Kitchen. 13. House hunting, 14. Lessors, lessees and their liabili- ties, etc. ^161 pages, 26 illustrations. i2mo., cloth, $1.00. Books mailed post-paid to any address on receipt of price^ 2l Metal Plate Work, ITS PATTERNS AND THEIR GEOMETRY. Also Notes on Metals, and Rules in Mensuration; for the use of Tin, Iron and Zinc-plate Workers, Copper- smiths, Boiler-makers, Plumbers and others. By C. T. MILLIS, M.I.M.E. Second Edition, Revised and considerably Enlarged. In producing the Second Edition of this hook, which unfortunately has been long delayed through pressure of work, the author feels con- fident that the addition of the seventy pages of new matter will add considerably to the value of- this work, besides bringing it well up to date. It has been his aim throughout this work to be as plain and practical as possible and to be a guide and workshop companion not only to the young mechanic but also a valuable help to the old and experiencod worker in metal-plate. The number of illustrations used makes this work very comprehensive and explicit. CONTENTS OF CHAPTERS. Classification. Introductory problems. Articles of equal taper or inclination of slant. Patterns for round articles of equal taper or inclina- tion of slant. Equal tapering bodies and their plans. Patterns for flat faced equal tapering bodies. Patterns for equal tapering bodies of flat and curved surfaces combined. Patterns for round articles of unequal taper or inclination of slant. Unequal tapering bodies and their plans. Patterns for flat faced unequal tapering bodies. Patterns for unequal tapering bodies of flat and curved surfaces combined. Patterns for miscellaneous articles. Metals; alloys; solders; soldering fluxes. Seams or joints. Useful rules in mensuration ; tables of weights of metals. Index. 377 pages, 314 illustrations, 12mo., cloth, $3.50. 22 PIOMENTS, PAINT AND PAIWTING- —BY— GEORGE TERRY. Contents of Chapters. I. Preliminary — Color, pigments. 2. Blacks.— General, animal, bone, Frankfort, ivory, lamp ; Unimportant blacks, — aniline, candle, charcoal, coal, cork, German, iron, lead, manganese, Prussian, prus- siate, Spanish, tannin. 3. Blues- — Cobalt, Coeruleum. copper, Bre- men, Caeruleum, smalts, lime, azurite, Peligot, verditer, indigo, manganese, Prussian, yellow prussiate, Antwerp, Bong’s, Brunswick, Chinese, Paris, Saxon, soluble, Turnbull’s, ultramarine. 4. Browns. — Asphalt, bistre, bone, Cappagh, Cassel earth, chicory. Cologne, man- ganese, mars, Prussian, Rubens, sepia, ulmin, umbers, Vandyke. 5. Greens. — Baryta, Bremen, Brighton, Brunswick, Chinese, chrome, cobalt, Douglas, emerald, Guidnet’s, Lokao, malachite, manganese, mineral, mitis, mountain, Paris, Prussian, Rinmann, sap, Scheele’s, Schweinfurth, terre verte, titanium, verdigris, verditer, Verona earth, Victoria, Vienna, zinc. 6. Reds. — Antimony, Vermilion, baryta, Cassius purple, Chinese, chrome orange, chrome, cobalt, cobalt pink, colcothar, Derby, Indian, lead, minium, oxide, Persian, Realgar, red lead, rouge. Venetian, vermilion. Victoria. 7. Whites. — baryta, blanc fixe, Charlton, China, clay, enamelled, English, gyp- sum, white lead, lime, lithophone, magnesite, mineral, Orr’s enamel, Paris, permanent, satin, Spanish, strontia, terra alba, whiting, zinc. 8. Yellows. — Arsenic, aureolin, cadmium, chrome, gamboge, king’s, Naples, ochres, orpiment, realgar, siennas. 9. Lakes. — Brazil-wood, carminated, carmine, cochineal, madder, yellow. 10. Luminous Paint. II. Examination of Figments. — Fineness, body or covering power, color, durability. 12. Vehicles and Dryers. — Generalities. Oils, — ground-nut, hempseed, candle nut, linseed, menhaden, poppy- seed, tobacco-seed, walnut, wood or tung, extraction of seed oils, dry- ers, litharge, cobalt and manganese benzoates, cobalt and manganese borates, resinates, zumatic dryers, manganese oxide, Guynemer’s dryer, l)oiled oil, manganese oxalate. 13. Paint Machinery. 14. Painting. — The surface, priming, drying, filling, coats, brushes, water colors, discoloration, composition, area covered, measuring, carriage and car painting, woodwork painting, iron painting, fresco painting, removing odor. Index. 392 Pages, 49 Illustrations, i2mo., Cloth, $3.00. 23 THE PRACTICAL POLISH & VARNISH MAKER. A TREATISE CONTAINING 750 PRACTICAL RECIPES AND FORMULJl, FOR THE MANUFACTURE OF Polishes, Lacquers, Varnishes and Japans, of all kinds, for Workers in Wood and Metal, and Directions for Using. By H. C. standage. o The purport of this book is to put into the skilled mechanics’ and amateurs’ hands the means whereby they can readily prepare their own polishes, varnishes, lacquers and japans. CONTF.NTS. Ingredients used in making polishes, lacquers, varnishes and japans. Directions for the filtering and bleaching of volatile varnishes and lacquers. Formulas for preparing polishes for wood. Formulas for polishing pastes, creams’ and renovators, &c. ; for furniture creams or French polishes ; for furniture oils. Revivers and renovators. Polishing agents for metals. Miscellaneous polishing compounds. Practical directions for polishing wood. Directions for repolishing. Processes for polishing furniture. To polish delicate cabinet and papier-mache work. To polish woods in the lathe. To renovate old furniture. A durable polish for ebony. To polish walnut. Waterproof finish for veneering. Wood finish. Wax polishing of floors. Polishing deal. To polish ebony. To put onegg shell irolish on wood. Polishing black woodwork. Polishing black and gold work. Polishing white and gold work. Dry shining. A good polish for walking canes and other hard wood. Water polish. Formulae forpolishing various metals and miscellaneous materials. To polish alabaster. To polish book-edges. To polish cellnloid. Friction polish. To polish bone, horn, ivory, marble and imitation marble. Formula for marble dressing or polish. To jrolish — a black marble clock, -irearl, piano keys, plaster of Paris work, quartz, shells, show cases, slate and vulcanite. To clean and xjolish silverware. Compoiind for waxing and polishing floors. Formulae for pre- paring lacquers for wood, metal, and other materials, and juethods of using same. Lacquers for commoner metals, and methods of lacquering them. Lacquering metallic surfaces. Varnishes and japans. Formiilae for producing volatile and fat varnishes. General notes concerning varnishes. Varnishes for woodwork in general. Special and miscellaneous varnishes. Varnishes for boots, shoes and leather. Mastic varnishes. Photographic varnishes. Varnishes for vioUns. Caoutchouc varnishes. Oil of txirpen- tine varnishes. Formulae for making, and lorocesses of using, japans for wood and metal. AVith complete index. 260 PAGES, I2MO., CLOTH, PRICE $2,50. 24 A F^RA.CXlCA.Iv TTRE:AXISE) ON THE STRENGTH OF RIRTERIHLS. INCLUDING THEIR Elasticity and Resistance to Impact. By THOMAS BOX. Third Edition. SYNOPSIS OF CONTENTS. Tensile Strain.— Rivited Joints. — Strength of punched and drilled plates, principles of riveting, riveted joints for girder work, chain riveting, steel joints for girder work, strength of steel rivets, space between rivets. Cohesion Applied to Pipes, — Strength of thin two lap welded tubes, general rules for boilers, boilers for very high pressures, factor of safety for boilers, rules for strength of thick pipes, tensile strength of thick cast iron. Strength of Chains, Ropes, Etc. Shearing Strain. — Crushing Strain.— Strength of Pillars — Theory of pillars, rules for cast iron, wrought iron and steel pillars of hollow, cylindrical, square, rectangular, X. L, and channel sec- tions. connecting rods, piston rods, and radius rods for steam engines; effects of incipient crushing and wrinkling. Connection of Pillars WITH Transverse Strains. — Theoretical strenght of cast iron, wrought iron, steel and timber pillars. Wrinkling Strain. — Trans- verse Stp.ain. — General rules, special rules for beams of various sec- tions, cast iron and steel beams, plate iron and lattice girders, tubular beam.s. “Similar” Beams — Examples of simnlar beams, general laws, ‘ ‘unit” girders. Connection of T ransverse and other Strains. — Roofs — Strains on roofs, strength of rafters, struts, tie-rods, keys, rivets, etc., curved roofs. Torsional Strain. — Theoretical laws, practical rules for torsional strength, shafting for ordinary machin- ery, marine engine shafts. Extension and Compression. — General statement of facts, cast iron, wrought iron, timber. Deflection ok Beams. — Form of curves of flexure, general rules for deflections, effects of modes of loading and section of beams, deflection with safe load. Torsional Elasticity — Modulus of Elasticity. — Permanent set, defect of elasticity manifested by set, wrought iron. Impact. — Resistance of beams, effect of inertia of beams, resistance as the weight of beam simply, high ratio of safe and breaking loads, sum- mary of remarkable laws. Collapse OF Tubes. — Factor of Sakety. Proof strain, determination of factor by test bars. Fatigue of Materials. — General principles, statical and Dynamic Fatigue. Ap- pendix. Index. 525 Pages, 27 Full Page and Folding Plates, 8vo., cloth, $7.25. 25 Graphic Statics, Geometry, Drawing. Ortliosfrapliic Projection. — An Elementary Treatise on Orthographic Projection ; being a New Method of Teaching the Science of Mechanical and Engineering Drawing. Intended for the Instruction of Engineers, Architects, Builders, Smiths, Masons, and Bricklayers, and for the Use of Schools. By W. Binns, C E. 130 pages, 60 illustrations, 23 large folding plates, 8vo., cloth. $3.50 Ditto. — Second Course, with some Practical Remarks on The Teeth of Wheels, The Projection of Shadows, Principles of Shading, and Drawing from Machinery. For the Instruction of En- gineers, Architects, Builders, Masons and for the Use of Science Schools and Classes. By W. Binns, C.E. 180 pages. 67 illustra- tions, 23 plates and tables, 8vo., cloth. l4*5o Xlic Klcmcnts of Orapliic Statics* By Carl Von Ott. Translated from the German by G. Sydenham Clarke. Con- tents : — Part I. — Composition of Forces. The Simple Beam. Reso- lution of Forces. Interior Forces of Stresses. Part II. — Braced Structures. Stress Diagram. Braced Beams, with Travelling Loads. The Arch. Part 3. — Elements of the Theory of Strength of Materials. 121 pages, 93 illustrations, i2mo., cloth. |i.5oj:. Xlic Principles of Orapbic Statics.— By Major G. S. Clarke. Contents of Chapters, i. — Graphic Arithmetic. 2. — Com- position and Resolution of Forces, etc.; Parallel Forces; Moments of Forces; Couples. 3. — Reciprocal Figures. 4. — Stress Diagrams. 5. — Action of Stationary Loads; Beams Fixed at One End; Beams Support- ed at Both Ends. 6. — Travelling Load. 7. — Braced Girders. 8. — Cen- tre of Parallel Forces; Centre of Gravity. 9. — Moment of Inertia; Central Ellipse, etc. 10. — Moment of Resistance; Central Ellipse, etc. Appendix. Tables. 142 pages, 1 18 illustrations and ii plates, 4to., cloth. $5.00 Practical Ocometry. — Perspective and Engineering Draw- ing. By G. S. Clarke. Chapter i. — Plain Geometry. Solid Geo- metry, 2. — Orthographic Projection. 3. — Lines and Planes. 4. — The Use of Indices. 5. — The Projection of Solids. 6. —Sections of Solids by Planes. 7. — Inter-penetration of Solids. 8.— Tangent Planes to Surfaces. 9. — Determination of Shadows. 10. — Shade-lines and Shadings. ii. — Isometric Projection. 12. — Perspective; En- gineering Drawings. 13. — General Considerations and Rules. 14. — Selection of Drawing Instruments, etc. Vol. i. Text, 175 pages, 102 illustrations, 8vo., cloth. Vol. 2. — Plates, 98 illustrations, 4to, cloth. Two vol’s complete, $4.00 Books mailed post-paid to any part of the World on receipt of price. 2t> TTME Commercial Organization of Factories. A Handbook for the use of Manufacturers, Directors, Auditors, Engineers, Managers, Secretaries, Accountants, Cashiers, Estimate Clerks, Prime Cost Clerks, Bookkeepers, Draughtsmen, Students, Pupils, &c., &c. By J. SLATER LEWIS. “The system of accounts presented in this book is the result of many years close observation and practical experience, and is, what may be termed an interlocking system, under which each and every account in a factory is brought into line monthly, and a general balance of the whole affected. It will be seen from an inspection of the dia- grams A and B, that the system is not only capable of diagrammatic proof, and may, therefore be relied upon as being complete ; but that it may be expanded or contracted as circumstances may require.” Stock Requisition-Note Guard-Book, eight pages of diagrams, large oblong. A large diagram of Manufacturing Accounts, i8q6, colored, 19^ X 27i inches. A large diagram of Balance Sheets, 1896, colored, 20 X 2yi inches. Large Folding plate Diagram of Manufacturers’ Accounts, 1896, colored. Folding plate. Staff Organization Diagram, 192 illustrations, diagrams, forms, orders, receipts, records, &c. Contracts and estimates. Travellers’ order forms. Bills of Exchange, &c., &c. Very full index. 540 pages, 4to., cloth, $ 12.00 CONT'EKTTS OK CK[A.KXKR.S. Introduction, i. — The Directors. 2. — The Manager. 3. — The Secretary. 4. — The Auditor. 5. — The Accountant. 6.— The Cashier. 7 —Correspondence Clerk. 8.— Sup- plies’ Orders and Invoices. 9. — Customers’ Orders and Invoices. lo. — Drawing Office. II.— Estimating. 12. — Stationery. 13. — Advertising and Catalogues. 14. — The Works. Manager. 15. — The Inspector. 16. — The Entrance Gates and the Gatekeeper. 17. — The Stores and Storekeeper. 18. — The Warehouse and Warehouseman. 19 — Carriage 20. — The Eoremen. 21. — The Time-keeper and Job Clerk. 22. — The Paying of Wages. 23. — Establishment Charges. 24. — Stock Surveys. 25. — Diagrams and Curves. 26. — Diagrams of Manufacturing Accounts and Balance Sheets. 27. — General View of Manufacturing Accounts. 28. — Synopsis of Transactions Relating to Purchases and Stores. 29. — Synopsis of Transactions Relating to Labor and Time. 30. — Synopsis of Transactions Relating to Manufacturing and Prime Costs. 3T. — Synopsis of Transactions Relating to Warehouse, Stock and Sales. 32. — Commercial Office ( Orders and Invoices.) 3^ — Stores. 34.— Works and Job Office. 35. — Warehouse. 36.— Prime Cost and Ledger Clerk’s Office. 37. — Balancing and Accounts. 38. — The Depreciation of Plant and Buildings. 39 —Re- cording Plant and Buildings. 40.— Foundry Accounts 41. — Forge Accounts. 42. — Pat- tern Shop Accounts. 43. — Salaries and Expenses. 44. — Agents and Travelers. 45. — Pupils. 46.— Apprentices. 47.— Shipping, 48,— Samples, Patterns, &c. 49.— Miscellane- oas. Appendix. Index. 37 Books by P. L. Simmonds. TTropical Agriculture. A treatise on the culture, pre- paration. commerce and consumption of the principal products of the vegetable kingdom. Section i. — Plants yielding seeds, leaves and other substances em- ployed in domestic use for the preparation of dietetic beverages, etc.: Cacas, guarana, kola nuts, coffee, tea, Yerba Mate, sugar, maple sugar, palm sugar, beetroot sugar, glucose or starch sugar, sorghum sugar, maize sugar. Section 2. — The useful plants and their eco- nomic products ; Coconut palm, African oil palm, gomuti palm, wild date palm (India), Palmyra palm, sago palm, bastard sago, Carnauba palm (Brazil), betelnut palm, betel pepper leaf, date palm, spiny date (Africa), wine or bamboo palm. Doum palm (Egypt), dwarf palm. Sec. 3. — The tropical serials and starch-producing plants : Indian maize rice, millets, sugar millet, broom corn, panicums, Italian millet, In- dian millet, shamay, sawa millet, cumboo or spiked, raggee, koda millet. Starch-producing plants. — Arrowroot, Tacca plant, Manioc or Cassava starch, the sweet potato, the yam tribe, the coco or eddoe, Japanese starches, chayote, potato starch and maize starch. Sec- tion 4. — The Principal Vegetable Dye Stuffs of Commerce. — Madder, munjeet, chay root, safflower, saffron, turmeric, cutch, gambier, annotta. Henna, alkanet root. Section 5. — The Oil Seeds AND Vegetable Oils of Commerce. — Olive, linseed, ground nut, cot- ton seed, castor oil plant, rape, mustard, curdee, sesame, niger, Ca- melina, sunflower, candle nut, Japan wax, poppyseed, melon, physic nut, croton oil, Chinese oils, oil of Ben, essential oils. Section 6. — The Principal Fruits OF Commerce. — Vine culture and the grape; dried fruits; products of the orange family ; pineapples, plantain, banana, fig, its culture and commerce, and other fruits. Seceion 7’ — The Spices of Commerce. — Pepper, chillies, ginger, nutmegs, mace, spice barks, cinnamon, vanilla, pimento, cloves, cardamoms’ Section 8. — Tobacco: Its production, uses and commerce. Index, 539 pages, 8vo, cloth. $8.oo| A Dictionary of Useful Animals and their products. A manual of ready reference for all those which are commercially important, and others which man has utilized. Including a glossary of trade and technical terms. 136 pages, i6mo, cloth, 80 cts. Xlae Animal Food Kesources of Dilferent Na- tionSy with mention of some of the special dainties of various peo- ple, derived from the animal kingdom. 461 pages, i2mo, cloth, $1.00. MopSf their cultivation, commerce and uses in various countries. A manual of reference for the grower, dealer and brewer. Contents of Chapters. — i. — History, botany, chemistry, 2. — Medical uses. 3. — Systems of cultivation. 4. — Cultivation. 5. — Qualities. 6. — Cultivation in Europe. 7. — Production in U. S. 8. — Culture in Australasia, g. — Bitter substitutes which have been used for the Hop, etc, " 135 pages with tables, i2mo. cloth, $1.25! Xhe Gras Engineer’s LABORATORY HANDBOOK. BY JOHN HORNBY, F.LG. Synopsis of Contents. Introdnctor j’' : — The balance ; weights and weighing. Sampling - mechanical division ; drying and dessicaiing ; solution and evapora; tion ; precipitation ; filtration and treatment of precipitates ; simple gravimetric estimates. Volumetric Analysis — Notes on the pre- paration of solutions. Indicators used in the volumetric estimation of acids and alkalis. Analysis by saturation. (Alkalimetry and acidimetry.) Preparation of normal acid and alkaline solutions. Processes of oxidation and reduction. Special Analyses E-equired in Gasworks. — Analysis of coal and coke. Estimation of the im- purities in crude gas. Testing purified gas for sulphur compounds, etc. Analysis of ammoniacal liquor. Analysis of li'me. Analysis of limestone. Analysis of oxide of iron. Analysis of spent oxide of iron. Analysis of fire clay and fire-bricks. Assay of coal tar. Frac- tional distillation. Determination of the specihc gravity of gas. Teclinical Gas Analysis. - Notes on the measurement of gases. Calibration of measuring tubes. The Hempel Burette. Hempel’s gas apoaratus. Double absorption pipette. Appendix.— Gas re- feree's instructions. Time and mode of testing for purity. Meters. Cubic foot measure, etc. Index. 304 pages, 03 illustrations and 36 pages of tables, lemo., cloth, I2.30. PRACTICAL HINTS ON THE CONSTRUCTION — AND— WORKING OF REGENERATOR FURNACES. BY MAURICE GRAHAM, C. E. Contents. Material. — Fire-clay, fire-brick, retorts, cement, mortar, hydraulic mortar, cement mortar, concrete, common brick, wrought iron, cast- iron. Gas-tight joints. Retort mouthpieces and lids. Furnaces and settings. — Foundations, footings, main piers, centering. Approx- imate rules for the thickness of arches and abutments. Chimney shafts. The producer. Air boxes. Regenerators. Analysis of producer gases before combustion. Analysis of water products in main flue. Fuel experiments. Bad heats. Summary. Advantages claimed on behalf of the gaseous firing system. Index. 131 pages, 50 illustrations, i6mo., liuip leather. $1.2^. 2g A PRACTICAL TREATISE CN As Applied to the Useful Arts for the Use of Engineers ^ Architects^ etc. BY XMOMAS BOX, CONTENTS OF CHAPTERS. I. General Principles and Data.— Unit of Heat ; Specific Heat of— Solids and Liquids, Air and Gases ; Liquefaction, Latent Heat of ; Ebulition; Latent Heat of Vaporization ; Expansion of Solids : Contraction of Metals in — Casting, Wrought Iron ; Expansion of — Liquids, Gases, Moist Air ; Thermometers ; Temperature of the Globe ; Sources of Heat and Cold ; Heat Developed by— Friction, Compression; Frigorific Mixtures; Density and Weight of Bodies; Atomic Weight of Bodies. II. On Combustion. — Theory of Combustion ; Heat Evolved in Combustion by — Theory, Experiment ; Air required for Combus- tion ; Products of Combustion ; Modes of giving out Heat usefully ; Tempera- ture of Air in Furnaces ; Means of obtaining veiy High Temperatures ; Radia- ting Power of Combustibles ; Combustion with Steam Boilers ; Relative effect of Long and Short Boilers ; Effect of Forcing the Fire ; Effect of too much Air ; Effect of too little Air. HI. On Steam Boilers. — Effective Heating Surface; Power of Boilers ; Boilers for Steam Engines ; Expansive Steam ; Water Heat- ers ; Superheating Steam ; Furnaces to Steam Boilers ; Fire-bars ; Safety- valves; Dampers; Area and Arrangement of Flues; Strength of — Steam Boilers, Boiler Tubes. IV. On the Efflux of Air, Etc,— Analogy of Efflux of Water; Velocity of Air, etc.— into a Vacuum, into Air; Coefficient of Con- tractions ; Friction of Long Pipes ; Square and Rectangular Channels , Effect of Repeated Enlargements and Contractions; Discharge of Steam; Steam- pipes to Engines. V. On Chimneys. — Chimneys to Steam-boilers; Round Chimneys ; Square Chimneys ; Effect of — Long and Short Flues, Internal Tem- perature. VI. On Vapors. — Elastic Force of Vapor; Mixtures of Vapor and Air ; Vapor in the Atmosphere ; Hygrometry ; Steam, Elastic Force of ; Elastic Force of Vapor of Alcohol, etc. VII. On Evaporation. — Evaporation in Open Air ; Effect of Wind on Evaporation ; Cold Produced by Evaporation ; Evapor- ation at High Temperatures ; Evaporating Pans ; Refrigerators ; Condensation Reservoirs to Steam-engines ; Dryness of Air, increased by Heat ; Evaporating Vessels for Stoves ; Evaporation at Boiling Point. VIII. On Distillation. — Principles of Distillation ; Condensing Apparatus. IX. ON Drying. — Drying — in Open Air, by Heated Air ; Proper Position of Inlet and Outlet Openings ; Drying— Closet for Linen, for Asylums, etc., at High Temperatures, in Closed Room, by Drying Cylinders. X. ON Heating Liquids. — Heating Liquids by — Fire Direct, Steam, at the top, Gas, Petroleum, etc. XI. On Heating Air, — Heating Air — Principles of, by Stoves; Heating by — Horizontal Flue-pipes, Vertical, Steam-pipes, Enclosed Pipes; Air-cocks; Apparatus for Condensed Water ; Expansion of Steam-pipes, etc.; Heating Air by Hot-water Pipes ; Ve- locity necessary to renew the neat'; Position of the Fire. XII. On THE TRANS- MISSION OF Heat and Laws of Cooling.— Loss of Heat by— Radiation, Con- tact of Air, Conduction, Buildings, Walls, Glass in Windows, Glasshouses; Effect of Covers on Cooling ; XIII. Laws of Cooling at High Tempera- tures. — Loss by — Radiation, Dulong’s Formula, Contact of Air, Dulong’s For- mula, Steam-Pipes, Enclosed Steam-pipes, Polished Metal Surfaces, etc.. Thick Cast-iron Pipes, Steam-pipes, cased. XIV. ON Ventilation. — Respiration; Air required for — Respiration, Carrying off Vapor, Exhalations, Carrying off Animal Heat, Lighting Apparatus; Methods of effecting Ventilation : Sufnmer and Winter Ventilation; Mechanical Ventilation; Ventilation ot— Schools, Chapels, Hospitals; Effect of different Combustibles in Ventilation. XV. Ex- amples OF Buildings Heated and Ventilated.— Prison Mazas ; Prison of Provins; Church of St. Roch — Particulars of. Temperature of Walls, Volume of Air, Time to Heat Building, Time to Cool Building, Heating Apparatus. XVI. On Wind, and its Effects on Ventilation, etc.— Influence of Wind on Ventilation ; Force and Velocity of Wind; Cowl for Chimneys; Form of Vane for Chimneys ; Stability of Buildings in Storms. Appendix. — Explosive Force of Gases ; Evaporation at Low Pressures of Air ; Absorption of Gases by Liquids ; Ice-houses. Index. 300 pages, 14 plates, 120 tables, i2mo., cloth, $5.00, 30 STANDARD MEASURES OF UNITED STATES, GREAT BRITAIN, AND FRANCE. BY ARTHUR S. C. WURTELE, Mem. Amer. Soc. C.E., ASS’T ENG.. N. Y. C. & H. R. R. A history of Standard Measures from their introduction in 1736 by the Royal Society to the present time, with actual comparisons of the Measures made at various times in the United States, Great Britain and France. Origin of the Metre and comparative results according to Delamhre, Bessel, Airy, and Clarke. Tables showing the reductions of the French Toise into English Feet, Metre in Inches, and length of the Seconds Pendulum as given by different writers. Appendix showing the disadvantages in practical use of the Metrical System, and the inconvenience attending its adoption, 8 VO, paper, price 50 cents. SPON & CHAMBERLAIN, PUBLISHERS, IMPORTERS AND BOOKSELLERS, 12 CORTLANDT STREET, NEW YORK. 31 HAND-BOOKS FOR Jeweiers, Watch and Cloekmakers. Britten, F. J. Former Watch and Clock-makers and Their Work, including an account of the development of horological instruments from the earliest mechanism, \vith portraits of masters of the art. And a directory of over five thousand names of famous watch and clock-makers, and some examples of modern construction. 397 pages, 187 illustrations, i2mo, cloth, 2.00 Watch and Clock-makers’ Hand-book, Dictionary and Guide. A complete description and explanations of all technical terms used in watch and clock-making; including a vocabulry of French and German terms, with their English equivalents. Eighth edition. 443 pages, 416 illustrations, 121110, cloth, 2.00 Neltliropp, Hev. H. Li. A Treatise on Watch-work Past and Present. 310 pages, 75 illustrations, 121110, cloth, 2.50 CONTENTS. A watch, definition of words and terms used in watch-work, tools required for watch- work, time, historical summary to the 15th, century, from A. D. 1500 to the present time, on calculations of the numbers for wheels and pinions, their proportional sizes, trains, etc., of dial work or motion work, length of time of going without winding up, the verge, horizontal or cylinder watch, the duplex, the lever, the chronometer or detached escapement, repeating watches, keyless watches, the pendulum, or spiral spring, com- pensation, jewelling of pivot-holes, Clerkenwell, fallacies of the trade, how to choose and use a w^atch, conclusion, appendix, index. Kemlo, F. Watch Repairers’ Hand-book. Being a complete guide to the young beginner in taking apart, putting together, and thoroughly cleaning the English lever and other foreign watches, and all American watches. By F. Kemlo, practical watch-maker. 93 pages, 6 illustrations, 121110, cloth, 1.25 Immiscli, Moritz. Prize Essay on the Balance Spring and its Isochronal Adjustments. 50 pages, i2mo, cloth, i.oo Kirkpatrick, T. S. G. Simple Rules for the Discrimination of Gems. 20 pages, 121110, French calf, .80 CONTENTS. Specific gravity, crystalline forms, cleavages, fracture, lustre, streak, rule for finding specific gravity, scale of hardness, curved edge of diamond, color of stones, valuable stones in river beds, electric test. ‘Rowell, Harvey. Manual of Instruction in Hard Soldering. With an appendix on the repair of bicycle frames, notes on alloys, and a chapter on soft soldering. Second edition, revised and enlarged, 66 pages, illus- trated, 121110, cloth, .75 See also Workshop Receipts, fifth series, 2.00 each. Cromwell, J. A System of Easy Letter. Containing 26 pages of al[)liabets of various designs. Oblong, 8 vo, paper cover, .50 Bool’S mailed post paid to any address on receipt of published price. 32 GETTY CENTER LIBRARY NH 510 T74 1897 ^ ^ Townsend. Chemistry tor photographers / 3 3125 00324 CONS BKS Charles F. 0153