THE DETERMINATION OF LACTOSE IN 
 
 MILK 
 
 BY 
 
 GEORGE CHARLES EBERT 
 
 THESIS 
 
 FOR THE 
 
 DEGREE OF BACHELOR OF SCIENCE 
 
 CHEMISTRY 
 
 COLLEGE OF LIBERAL ARTS AND SCIENCES 
 
 UNIVERSITY OF ILLINOIS 
 
 1922 
 
Finley 
 
 (T> 
 
 3 
 
 iSt'L 
 
 UNIVERSITY OF ILLINOIS 
 
 192 
 
 THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY 
 
 ENTITLED 
 
 IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE 
 
 DEGREE OF 
 
 ^lIIc 
 
 ■ .t ; ^ C X ^ .Li C G > • 
 
 Approved 
 
 ed:. .MAIG. 
 
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 9 - 
 
 HEAD OF DEPARTMENT OF 
 
 Instructor in Charge 
 
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 Digitized by the Internet Archive 
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AGElIOwXEDGLIEllIT 
 
 This inYestigation was unde rt alien upon 
 the suggestion and under the supervision of Dr. 
 Duane T. Snglis, to whom the author owes bis 
 sincere apiDreciation for the helpful suggestions 
 and encouragament given as the worli progressed. 
 
- THE HETSRI.:ilTATI011 CP lAOTCCE IIT IHXK - 
 
 Introduction and History 
 
 Tha inportanca of determining milk sugar or lactose in 
 nilk analysis was recognized as far kack as 1876. In tha de- 
 conpcsition of milk, lactose suffers a change and so causes a 
 decrease in amount of total solids present, Tha lactose is 
 transformed to lactic acid thus causing discrepancies in analysis 
 of stale milks, 
 
 I,Iilk is one of the important articles of human diet 
 aied So should not ha allowed to ha adulterated. A proper stan- 
 dard for the quality of cow*s milk should he acceptad. 
 
 There has haan ciuita a large amount of work done on 
 tha determination of lactose hy volumetric, gravimetric and op- 
 tical methods, some of which will ha here outlined. 
 
 In 1880 Huter f^inalyst 5:35j answers two (luesticns that 
 had often haen asked about lactose da tem'-inations and which are 
 answered differently hy different T^-orkers, They are, first, 
 what is tha hast method for an analyst to follow and secondly, 
 given such a method, what is tha true acj.iiivalent for calculation 
 of results? After q.uite extensive work Huter concludes that tha 
 hesi/ iDrocass for general use is the gravimetric method and that 
 it should ha carried out according to strict rules so as to en- 
 sure a constant equivalent and that tha precipitate may ha 
 weighed directly as cuprous oxide fCug^c). 
 
 f 
 
 Soma workers have contended that tha volumetric process 
 in which a small amount of sugar solution is brought into contact 
 

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 with strong a-lkali until an and point is raachad, is tha most 
 rapid, iluter thought and the same theory has hean held hy 
 others, that tha volurnatriG method never gives really accurate 
 results except hy accident. A truly constant equivalent cannot 
 “be ensured unless the whole can he diluted to such a point as to 
 render the alliali harmless, while the Cablings solution is at 
 once added in sufficient quantity to ins tantsjiecusly perform tha 
 entire reaction. Both tha sugar solution and the Fahlings solu- 
 tion should he boiling when mixed and these points cannot ha ob- 
 tained except by the gravimetric method. 
 
 It is held by some that cuprous oxide is not stable and 
 should be converted to the cupric state before weighing. The 
 cuprous oxide should be precipitated from a boiling solution and 
 washed with boiling water so as not to allow long e:cpoEura to tha 
 air. If than two drops of petroleum ether are placed on tha pre- 
 cipitate and the crucible placed in a good close drying chamber 
 at temperature of boiling water, the cuprous oxide is a more con- 
 venient and accurate article for weighing than the varj- hygros- 
 copic cupric oxide. 
 
 I'iuter found by accurate checking that the true equival- 
 ent is 146.3 parts of cuprous oxide to every 100 parts of lactose, 
 providing the precipitate is not allowed to stand in the solution 
 for any length of time. 
 
 In 1884, E. E. Eiley (Aualyst IS: 174; ihin. Cham. Jour. 
 
 6; S89) Chemist of the Enited States Department of Agriculture anc. 
 later head of the Bureau of Chemistry, published a vary good work 
 on the specific rotation of milk sugar and tha classification of 
 
 ■,71ien crystalline milk sugar is first 
 
 milk for polarisation. 
 
o 
 
 clissclvad it giv0S a higher rotatcrj^ power than it had in the 
 milk frcn which it wac derived. After standing for 12 - 20 hours 
 or immediately on hoiling this omtra rotation is lost. The 
 various values published for the specific rotatory power of lac- 
 tose always refer to the constant rotatory power and not the 
 variable. After thorough investigation, T7iley accepted the 
 value obtained by Schiaoager, as = 52.53^ for sxoocific rota- 
 tion of lactose. This figure has stood the test as it is the 
 value generally used to the i^rasent daj*. 
 
 In order to ha-ve an optical method which is satisfactoiy 
 soma means of clarifying the milk solution must be worked out. 
 
 All of the albumens and other laevo-rotatcry compounds must be 
 removed from the milk, leaving a clear colorless filtra.te, before 
 polarisation can be carried out. As clarifiers TTilej/' used: - 
 
 1) Saturated solution of basic lead acetate, sp.gr. 1.97. 
 
 2) nitric acid solution of mercuric nitrate diluted with 
 an aoual volume of water. 
 
 3) Acetic acid, sp.gr. 1.04, containing 29^b acetic acid. 
 
 4} nitric acid, sp.gr. 1.197 containing 30^a nitric acid. 
 
 5} Sulphuric acid, sp.gr. 1.255 containing 30^ sulxohuric 
 
 acid. 
 
 6) Saturated solution llaCl. 
 
 7) Saturated solution IlgSCA* 
 
 8) Solution of mercuric iodide in acetic acid; formula: - 
 ILl 33.2 grams; HgOl 13.5 grams; strong acetic acid 20 cc. ; 
 water 640 cc. 
 
 Tliley also used other agents for clarifying, as solutions of min- 
 

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 aral salts such as copper sulfata, and hydrochloric and other 
 acids. The last he did not deem of any use what aver. Acids 
 and alkalies seem to increase the rotating power. He showed 
 that any great excess of "basic lead acetate caused a considera"ble 
 decrease in rotatory poY/er. It is not clear whether this 
 decrease is due to solution of the alhurnens or precipitation of 
 the sugar. It seams to make very little difference if the pre- 
 Gip)itation is carried out in the hot or cold "but the readings of 
 the polariscopa must "be taken at SO^G. By ccm"busticn with soda- 
 lime the quantity of laevo-rotatory matter, calculated as nitro- 
 gen, remaining in the filtrate after treatment with "basic lead 
 acetate is much greater than that left after treatment with mer- 
 curic iodide. This eirplains the higher results o"b tanned when 
 using the mercury salts and shows that the "basic lead method 
 should "be a"bandcned as a method of clarification. Hiley decided 
 that the "best clarifying agents were 1 cc. acid mercuric nitrate 
 for 50 cc. milk; or else 25 - 30 oc. mercuric iodide for 60 cc. 
 milk. An excess of the mercuric salts does no harm and the pre- 
 cipitation may easily "be carried out in the cold. In all cases 
 Hiley allowed 2 cc. for 50 cc. milk for volume of precipitated 
 casein. 
 
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 the estimation of car"bohydrates in milk, admits that Br. Hiley*s 
 method of clarification By mercuric nitrate or iodide is a very 
 good one. However, he o"bjects to the procedure on the groumds 
 that the solutions cannot then "be used for o.ny other purpose than 
 polarime trical o"bservations. That is, no other determinations 
 can "be made on this solution. If a shadow instrument is used an 
 
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 almost clear whey can "be obtained, by precipitation with copper 
 sulfate and. if the proper amount is used the filtrate is so pale 
 a blue as not to interfere with the reading. HLyth seems to 
 have been the first investigator to attempt this. This solution 
 can then also be treated with Pehlings solution and the regular 
 copper reduction method followed gravimetric ally. 
 
 The method of clarification finally adopted by Hyth 
 for precipitating the casein was by acetic acid. S5cc. of milk 
 was diluted to about 50 cc. with distilled water and then strong 
 acetic acid added drop by drop until the casein begins to separ- 
 ate. The liquid is then heated to boiling and whirled in a 
 centrifugal machine. The casein, albumen, coagulated serum and 
 fat are collected at the bottom, while the supernatant fluid is 
 easily filtered. The precipitate is washed, the filtrate cooled 
 and made up to 100 cc. This solution can then either be polar- 
 ized or have a copper reduction da termination run on it. The 
 filtrate is usually of a feeble yellow color, but perfectlj/ 
 bright and suitable for testing for substances such a.s salicj’-lic 
 acid, borax, dextrin or any soluble addition. 
 
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 18S) worked out a method of determining lactose by double dilutior 
 and subsequent polarization. The figure formerly accepted by 
 T7iley for the volume of precipitate, as S ce. for 50 cc. of milk, 
 was thought to be somewhat in error. To overcome this error 
 these two investigators worked out the following double dilution 
 method. The clarifying agent used was acid mercuric nitrate, 
 and the polarization was carried out in a triple -field shadow 
 polariscope of the Schmidt and Haensch type by which readings 
 
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 accurate to .05 of one percent mojr i)e taken. The flasks used 
 were 100 and SOO cc. carefully calilirated. The same amount of 
 milk, that is double the normal weight for the instrur.ient, was 
 used in each flask, clarified and polarized. xill readings were 
 made in duplicate by both Vv'orkers in a 400 mm. tube in order to 
 gat the most accurate results. The temperature of the working 
 room was kept at about S0°C. since the rotation of lactose in- 
 creases notabljT- with rise in temperature. 
 
 By means of the following algebraic equations ITiley and 
 Ewell work out the correct volume of the precipitate and the 
 correct reading of the polarisccpe: 
 
 let x= voluTiia of precipitate 
 y= correct reading 
 a= reading from the small flask 
 b = reading from the large flask 
 Then, SOO — x : 100 — x ; : a : b 
 SOO b — bx= 100 a— ax 
 
 ( 1 ) 
 
 X — a — b 
 
 100 (a— S b) 
 
 correct volume of precipitate 
 
 100 —X ; 100 : : y : a 
 
 : 100 : : y ; a 
 
 y = a- 
 
 a(a — 3b) 
 a — b 
 
 ( 2 ) 
 
 a^— ab — a^-4- 2ab 
 
 5^= a”-=-^5 
 
 correct reading. 
 
 Rule (3) stated in words is that the true polarization as deter- 
 mined by double dilution is found by dividing the product of the 
 
7 
 
 t\7o readings in the large and small flasks their difference. 
 
 According to 7iley end lUn'all this method ta}:es vary 
 little more time than a single polarisation and should he used at 
 all times when an accurate determination is to he made, instead of 
 correcting for the volume of precipitate hy any arbitrary factor. 
 
 - In 1913 there appeared an article hy TTalker and Aarsh, 
 
 ( J. A. 0. S. 35: 8S3] in which they used aluminum hydroxide as 
 the clarifying agent in lactose determinations. The reagent was 
 made hy precipitating aluminum hydroxide from a solution of 
 ammonium alum with ammonium hydroxide and washing hy decantation 
 till pure. The aluminum hydroxide was finally centrifuged and 
 the thick jelly obtained made somewhat thinner hy agitation with 
 w'atar. In using this reagent the authors obtained results very 
 close to those obtained hy the copper-alkali method and the fil- 
 tration was much easier. ija excess of reagent does not influence 
 the results whatever. 
 

 
 
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 In this investigation the samples of milk, all of 
 which were very kindly furnished hy the dairy department of the 
 College of Agriculture at this University, v;ere first analysed hy 
 the official optical Q. A. 0. method, mercuric nitrate heing 
 used as the precipitant. The result hy this method w:,s used as 
 a guide for tue other methods tried us this has keen accepted as 
 a standard. 
 
 The reagent v;as prepared ky dissolving mercury in 
 dcukle its weight of nitric acid, (sp.gr, 1,42} aaid diluting with 
 
 . volume 
 
 of distil 
 
 led 
 
 water. 
 
 For the amount 
 
 of milk 
 
 CG. 
 
 was 
 
 found to 
 
 ke £ 
 
 iufficient to furnish 
 
 an 
 
 ezeess. 
 
 'ity 
 
 of milk 
 
 to ke 
 
 used varies 
 
 with the sp( 
 
 3Cific gravitjr 
 
 the 
 
 type of 
 
 polar 
 
 iscc 
 
 p3 used. 
 
 
 
 
 Sp. 
 
 gr. 
 
 of L 
 
 a Ik 
 
 
 Ycl. 
 
 of milk to 
 
 ke 
 
 used 
 
 
 
 
 
 
 for 
 
 pol arise ope 
 
 whose sucrose 
 
 
 
 
 
 
 nom 
 
 lal weight is 26.048 grams, 
 
 
 1. 
 
 024 
 
 • • 
 
 • 
 
 . . 
 
 64,4 cc. 
 
 
 
 
 1. 
 
 026 
 
 • 
 
 • 
 
 • . 
 
 64.3 
 
 
 
 
 1. 
 
 028 
 
 • 
 
 • 
 
 • • 
 
 64.15 
 
 
 
 
 1. 
 
 030 
 
 • 
 
 • 
 
 • • 
 
 64.00 
 
 
 
 
 1. 
 
 032 
 
 • • 
 
 • 
 
 • . 
 
 63. 90 
 
 
 
 
 1. 
 
 034 
 
 • 
 
 • 
 
 • . 
 
 63.80 
 
 
 
 
 1. 
 
 035 
 
 • 
 
 • 
 
 • . 
 
 63.70 
 
 
 
 The 
 
 qua 
 
 ntit 
 
 y of milk 
 
 indicated is placed 
 
 in 
 
 a flask 
 
 at 
 
 102. 
 
 6 cc 
 
 . for 
 
 a Yi 
 
 antsiia, o 
 
 r 102.4 for , 
 
 a n 
 
 aurent po- 
 
 • 
 
 8.5 
 
 GG. 
 
 acid 
 
 mer< 
 
 eurio nit 
 
 rate and 3.5 
 
 cc 
 
 . alumina 
 
a 
 
 
 
 
 wim 
 
 \ 
 
 
 
 iLk « 
 
9 
 
 crGon, to help in tho clari fioati on are adcled. The Hack is 
 filled to tl]e nark ";ith distilled water, a£;itated, filtered 
 through a dr;^ filter and polarised. TThen using a 200 nm. tube 
 the reading is to he divided hy 2 if the sucrose normal weight is 
 26.048. 
 
 The optical method was also studied, anhydrous basic 
 lead acetate being used as the clarifying agent in this method. 
 2-3 grams of this salt was sifted into the flask containing the 
 milk and 3 cc. of alumina cream a.dded. The flask was then filled 
 to the mark with distilled water, filtered through a dry filter 
 and polarized the sanie as in the preceding method. 
 
 In the gra,vimetric n. 0. A. G. , 25 cc. of milk is di- 
 luted in a 500 cc. flask to 400 cc. with distilled water and 
 10 cc. of a Solution of copper sulphate added, this. copper sul- 
 phate of the strength given for Soxhlet*s modification of the 
 Pehlings solution, which is 69.378 grams of OuS 04*5 FgG in one 
 liter. About 7.5 cc. of a solution of potassium hydroxide is 
 added of such strength that one volume of it is just sufficient 
 to completely ]precipitate the copper as hj'drcxide from one volume 
 of the solution of copper sulphate. Instead of potassium 
 hydroxide 8.8 cc. of half normal sodium hydroxide nay be used. 
 After the addition of the alkali solution the mixture must still 
 have an acid reaction and contann copper in solution. The flask 
 is filled to the 500 cc. mark, agitated and the solution filtered 
 on a dry filter. 
 
 In this filtrate the la-ctcse is determined by copper 
 reduction method. 50 cc. of mixed copper I'ehlings reagent is 
 placed in a beaker and heated to the boiling point. 7hile 
 
u 
 
 f . ‘ ^ 
 
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10 
 
 TDoiling iDrislily, 100 gq. of the lactose scliiticn is added and 
 "boiled for six minutes, immediately filtered through an asbestos 
 Gooch crucible and washed with hot water, 10 cc. ethyl alcohol, 
 o-nd 10 cc. ethyl ether. The precipitate is dried at lOO^’O. and 
 weighed as cuprous oxide. The percentage of lactose is calcu- 
 lated from the Soxhlet and TTein table for lactose. 
 
 The chief difficulties in the gravimetric method here- 
 tofore have been the very slow fil.tration, and the acid concen- 
 tra.tion of the solution to effect good precipitation. The 
 author has attempted to overcome these difficulties in this worlr. 
 The procedure of the A. L. C. was somewhat modified \Tith this 
 in view. 
 
 In a 500 cc. flasli, 25 cc. fo milk are placed and di- 
 luted to 400 cc. with distilled Water and 10 cc. of copper sul- 
 phate solution added of the strength used in the x*. C. A. 0. 
 method. Then 2 or 3 drops of phenolphthalein are added as in- 
 dicator. Half normal sodium hydroxide is dropped in slowly till 
 the solution is left just barely acid. If the end point is 
 over-run slightly it is brought back with a few drops of dilute 
 sulphuric acid without seeming to effect the results in any way. 
 The solution is diluted to 500 cc. and shalcen well. Part of 
 this solution is next transfered to a SOO cc. centrifuge bottle 
 and whirled in a centrifugal machine for 20 - 30 minutes at about 
 800 R. P. 11. At the end of this tim.e the precipitate is q.uite 
 tightly packed in the bottom leaving an almost clesji supernatant 
 liquid. This supernatant liquid is then run through a diy 
 filter and the resulting filtrate used in method explained above. 
 
 It w'as a,lso found that this filtrate could be quite 
 
11 
 
 easily polarized just as when acid mercuric nitrate is used as a 
 clarifying agent. The copper left in solution after treating 
 hy this procedure is of such a small ausntity as not to color 
 solution sufficiently to prevent reading of the polariscope. 
 
 

 
 
 
 
 
 1-2 
 
 
 
 -LATA- 
 
 
 
 
 SAI'.-IL3 
 
 - ■ ■ ■ 
 
 — 
 
 
 
 ' " 
 
 
 imxBSH 
 
 I 
 
 - - 
 
 II 
 
 III 
 
 lY 
 
 Y 
 
 YI 
 
 Specific 
 
 
 
 
 
 1.032 
 
 Gravity 
 
 1.030 
 
 1.0304 
 
 1.0354 
 
 1.0308 
 
 1.028 
 
 1 
 
 HgdTOgjg 
 
 9.05 
 
 9.05 
 
 9.67 
 
 9.24 
 
 9.84 
 
 9.34 
 
 ( reading) 
 
 9.27 
 
 9.09 
 
 9.65 
 
 9.32 
 
 9.20 
 
 1 9.50 
 
 percent 
 
 4.525 
 
 4.525 
 
 4.835 
 
 4.62 
 
 4.85 
 
 4.67 
 
 Lactose 
 
 4.58 
 
 4.635 
 
 4.535 
 4 , 54& 
 
 4.83 
 4^025- - 
 
 4.64 
 
 4.66 . - 
 
 4.76 • 
 1 4,a7 
 
 4.71* 
 
 -4.75- 
 
 Anhydrous 
 
 8.22 
 
 8.04 
 
 8.42 
 
 8.82 
 
 8.36 
 
 sample 
 
 lead acetate 
 (reading) 
 
 8.34 
 
 7.94 
 
 8.22 
 
 9.06 
 
 8.60 
 
 lost 
 
 Percent 
 
 4.11 
 
 4.02 
 
 4.21 
 
 4.41 
 
 4.18 
 
 
 4.14 
 
 3.995 
 
 4.16 
 
 4.47 
 
 4.24* 
 
 
 Lactose 
 
 . — _ 
 
 ^4.17 
 
 3.97 
 
 . 4.11 __ 
 
 4.53 
 
 4.30 
 
 
 Clarified with 
 
 copper sulphate and sodium 
 
 hydroxide 
 
 
 optical 
 
 . 69 
 
 .68 
 
 .744 
 
 
 .719 
 
 .721 
 
 Headings 
 
 .71 
 
 .69 
 
 .741 
 
 .705 
 
 .736 
 
 .720 
 
 Percent 
 
 4.416 
 
 4.363 
 
 4.752 
 
 4.55 
 
 4.615 
 
 4.613 
 
 4.445 
 
 4.392 
 
 4.74 
 
 4.531 
 
 4.67 
 
 4.607* 
 
 Lactose 
 
 4.473 
 
 4.421 
 
 4.728 
 
 4.512 
 
 4.725 
 
 ; 4.601 
 
 Height 
 
 ■ 
 
 .3750 
 
 .3676 
 
 . 3934 
 
 .3857 
 
 .3770 
 
 .3761 
 
 CugO 
 
 .3741 
 
 .3728 
 
 .3971 
 
 .3722 
 
 .3961 
 
 ' .3891 
 
 Height 
 
 . 2996 
 
 .2928 
 
 .3139 
 
 .3079 
 
 .3080 
 
 ; . 3008 
 
 Gu 
 
 . 2989 
 
 .2972 
 
 .3164 
 
 .2969 
 
 .3161 
 
 .3102 
 
 percent 
 
 4.48 
 
 4.391 
 
 4.698 
 
 4.61 
 
 4.615 
 
 14.512 
 
 
 4.475 
 
 4.42 
 
 4.728 
 
 4.528 
 
 4.681 
 
 1 4.58^^ 
 
 Lactose 
 
 4.47 
 
 4.449 
 
 4.758 
 
 4.446 
 
 4.747 
 
 !4.648 
 
 * Averages. 
 
13 
 
 - DISCUSSICII - 
 
 !Prom the tahles of data it can "be seen that the results ^ 
 secured hy the use of hasic lead acetate were rather unsatisfac- 
 tory. HcVifeYer, this was to he eir-.ected since this i:)rocedure has 
 never appeared to give satisfactory results with other investi- 
 gators. ihe quantities indicated hy this method were all con- 
 siderably lower than those obtained by using mercuric nitrate. 
 
 Vary good check results were obtained by using' the 
 modified copper sulphate clarification procedure. lha percen- 
 ta,ges of the gravimetric method and the polarimetric determination 
 check vary closely with each other although they are about one 
 tenth of one percent lower than the results of the A. g. A. G. 
 method. These may be low due to not having complete precipita- 
 tion of the dextro-rotatory nitrogen compounds when acid mercux'ic 
 nitrate was used for this purpose. 
 
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 - a.* ;^: , |, i« 6 : '*ii'i ' ^iV'l Q J ,,i j 4-1 ^ ^ r^’ ^ W ' >' . 
 
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 U'^(l stdi-Vy^'i^ ■ -4 '' 's/iao 
 
 ^ 1 ■ ' . (V ' V ' * ^ ^ 
 
 ,. i,' „ k' 1*1 i‘ n'^' j" 'i- .„, . 
 
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 '■' j ■%. ' "I - k. I.** ■' '■ ‘ V ' V' 
 
 : ' "^ "' i, . 1 A',*: 
 
 ,“■ i[ ''-i A>iki'i’A' S’4‘''^ ‘/ui' iv’ ■ii/nS' , ", 
 
 "fe-V-lt 'I 
 
 ,' . : .' : 5 Hf jisiE; v.Miiifci: '1 
 
 'r^A' ‘"f ';■!<«*• 
 
 rv,>-'- mm 
 
 r.';„,By’_ ..- , '.l 'iJ,,:tmS ■aSui*' ...» a« : . 
 
 *v -•>■ 
 
 I . X I .y. 
 
 a ;: ,,•. *.'r ■:•« 
 
 ,. .. , „ ,, ,_, 
 4 . ’ I ' I , ’ V *tfj- . •.I' .1^' f .. ' / 'li ' - 
 
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 i»r 4 ’■. ' I’:". 
 
14 
 
 -SUMHART- 
 
 1. This study was undertaken with the ohjeot of 
 determining a more efficient method of adjusting the acid 
 concentration of solutions of lactose after clarification 
 with copper sulphate, and ox determining a more rapid 
 method of filtration. These have heretofore heen the 
 chief difficulties in lactose determinations. The diffi- 
 culty of acid concentration is easily overcome "by using 
 phenolphtha-lein as an indicator. 
 
 S, The inability to secure a rapid filtration 
 after the clarification has been eliminated bj^ centri- 
 fuging the solution before attempting filtration. The 
 supematsjit liquid is then verj- easily filtered. 
 

 '^4 
 
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 ^'1 
 
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 ■ ■ : , ’ 4% i.0*4'* . f; mmM&k 
 
 
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 ■'• ' ■ ■ '■'®: . ■■' ^'7^'"' ‘ 7^JW^’' »«» ' ■ « 
 
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 Si :Lj y ■ >' ^-ji^*!:.' ,>jM)l||^ ‘ ■'• i^^K|Q| 
 
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 •fi<M ' , ^»^.y i' '• m 
 
 ‘.V 
 

 - B I B L I C 
 
 G H A P H 
 
 r ^ 
 
 
 1. 
 
 iim. Gharn. Jour. 
 
 • . 6 : 
 
 289 
 
 (1884) 
 
 2. 
 
 Analyst 
 
 . . 5: 
 
 35 
 
 (1880) 
 
 3. 
 
 Analyst . 
 
 . . 8 ; 
 
 243 
 
 (1883) 
 
 4. 
 
 Analyst 
 
 9: 
 
 116 
 
 (1884) 
 
 5. 
 
 xinalyst 
 
 . 10: 
 
 62 
 
 (1885) 
 
 6 » 
 
 ilnalyst 
 
 . 11: 
 
 28; 
 
 141 (1886) 
 
 7. 
 
 iinalyst 
 
 12: 
 
 176 
 
 (1887) 
 
 8. 
 
 Analyst 
 
 13: 
 
 63 
 
 (1888) 
 
 9. 
 
 xinalys t 
 
 . 20: 
 
 121 
 
 (1895) 
 
 • 
 
 o 
 
 H 
 
 iinalyst 
 
 21: 
 
 162 
 
 (1896) 
 
 11. 
 
 Analyst . 
 
 22: 
 
 98 
 
 (1897) 
 
 12. 
 
 iinalyst 
 
 . 26 : 
 
 127 
 
 (1901) 
 
 13. 
 
 imalyst 
 
 . 35: 
 
 516 
 
 (1910) 
 
 14. 
 
 Bulla tin 107 U. S. 
 
 Gbernistr^:" 
 
 Bureau 
 
 15. 
 
 Jour, of iiX-i* Gbem. 
 
 See. 15: 
 
 694 
 
 (1893) 
 
 16. 
 
 Jour, of iijfl. Giaem. 
 
 SoG. 35: 
 
 823 
 
 (1913)