THE HYDROLYSIS OF TERTIARY 
 ARSENATES 
 
 BY 
 
 HAROLD BYRON JOHNS 
 
 THESIS 
 
 FOR THE 
 
 DEGREE OF BACHELOR OF SCIENCE 
 
 TN 
 
 CHEMICAL ENGINEERING 
 
 COLLEGE OF LIBERAL ARTS AND SCIENCES 
 
 UNIVERSITY OF ILLINOIS 
 
 1922 
 
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/922 
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 UNIVERSITY OF ILLINOIS 
 
 . - PS.J 1 92 s . 
 
 THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY 
 
 lA _ _£ YHPJ0-. A oJins 
 
 ENTITLED _ c_f_X©_rtJ.axy__Ar_aejaaJLes^ 
 
 IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE 
 
 DEGREE OF a.QLe LQC--QL-Cjiii3xg-Q-ia-Siiei'iiC-aI--KrLg1 ne r r i . n 
 
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Acknowledgement 
 
 The writer wishes to express his deep feel- 
 ing of gratitude to Dr 0 J.H, Reedy, whose careful su- 
 pervision made this work possible, and to thank him 
 for the assistance, which he so generously gave at 
 all times. 
 
Digitized by the Internet Archive 
 in 2015 
 
 https://archive.org/details/hydrolysisoftertOOjohn 
 
Table of Contents . 
 
 Page 
 
 I . Introduction 1 
 
 (a). Pacts suggesting the problem 1 
 
 (b ) . Pteview of the literature 2 
 
 (c). Statement of the problem 3 
 
 II. Theoretical 3 
 
 (a) . Effect of colloidal dispersion on 
 
 the toxicity of an insecticide 3 
 
 (b) . Permanence of suspension 3 
 
 (c) . Protective effects against weathering 3 
 
 III . Experimental 4 
 
 (a) . Preparation of the colloid 4 
 
 (b ) • Preparation of other arsenates 5 
 
 (c) . Determination of the solubilities of 
 
 the arsenates 6 
 
 IV. Summary 8 
 
 V, Bibliography , 10 
 

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1 . 
 
 I. 
 
 Introduction. 
 
 (a). Facts suggesting the problem. 
 
 Lead arsenate has been used as an insecticide for several 
 years. On account of the increased cost of manufacture, how- 
 ever, manufacturers have recently directed their attentions to 
 the manufacture of a substitute, calcium arsenate, which can be 
 produced for about one half the cost of the lead arsenate. 
 
 Calcium arsenate is now being manufactured in large quan- 
 tities and is used in the south, principally for the destruc- 
 tion of the cotton boll worm and, to a lesser extent, for the 
 tobacco worm, Colorado potato beetle, and the codling moth. 
 
 It has been conclusively demonstrated that these two arsenates 
 are equal in toxic value and killing power. 
 
 There is one great disadvantage in the use calcium arsen- 
 ate as an insecticide in that, even though the product may be 
 free from water soluble arsenic when it leaves the factory, it 
 very often has an appreciable of water soluble arsenic when it 
 reaches the consumer. This water soluble arsenic burns the 
 foliage of plants and since it cannot be removed, large amounts 
 of the insecticide are returned and cause a great loss to the 
 manufacturer. Another disadvantage is that many batches are 
 spoiled in preparation because of the difficulty of properly 
 controlling the conditions of formation. 
 
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2 . 
 
 (b ) , Review of the literature. 
 
 Reedy and Haag (l) found that the presence of such impu- 
 rities as HaCl or FeSO^ seemed to catalyze the formation of wa- 
 ter soluble AS 2 O 5 , Exposure to air and carbon dioxide had sim- 
 ilar effects . 
 
 De Toni ( 2 ) recently prepared colloidal tri -calcium phos- 
 phate by adding slowly and with constant stirring, nearly boil- 
 ing N Na^PO^ solution, largely diluted, to an equal volume of 
 hot N GaGlg, which also had been largely diluted and had been 
 mixed with the desired quantity of gelatin as protective col- 
 loid. He found that cold solutions react slowly and remain 
 clear for a long time. By adding the phosphate to the calcium 
 chloride an excess of Ga ions is assured and the formation of 
 tri -calcium phosphate* Gelatin gives a precipitate with the 
 sodium phosphate and is therefore added to the calcium chloride. 
 De Toni prepared the Na^PO^ solution by adding the calculated 
 amount of NaOH to a solution of Ha 2 HP 04 , diluting to normal and 
 then carefully protecting from the air. By varying the concen- 
 trations he found that to make colloidal solutions containing 
 2.068, 3.102, 4.137 g. Ga 3 (P 04)2 in 1000 cc. none of which would 
 show a precipitate, there were required, respectively, 9.5, 17.0, 
 and 27.5 g. of gelatin. He found that gum arabic, blood serum, 
 and starch may be used as protective colloids, but sugar and 
 caramel do not give colloidal tri -calcium phosphate. 
 
3. 
 
 (c). Statement of the* problem. 
 
 Since there is a possibility that a precipitate in col- 
 loidal form would not be so apt to hydrolyse, the purpose of 
 this research was first, to try to prepare colloidal tri-calcium 
 arsenate; second, if this colloid is obtained, to study its sta- 
 bility and ionization; and third, to study the stability and ion- 
 ization of other tertiary arsenates. 
 
 II . 
 
 Theoretical . 
 
 (a). Effect of colloidal dispersion on the tox- 
 icity of an insecticide. 
 
 Burton (3) found that the average diameter of the colloid- 
 al particles of gold, silver, and platinum range from 0.2 to 0.6 
 micron and other colloids are known to have particles that are 
 only one millimicron in diameter. These particles are therefore 
 much smaller than the particles of an ordinary precipitate which 
 is in suspension. Hence, since we have increased solution and 
 smaller particles, the toxicity of an insecticide should be in- 
 creased when it is in a colloidal form. 
 
 (b ) . Permanence of suspension. 
 
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 Tfhen peptized, colloids remain suspended or disbursed for 
 an indefinite period of time. On the other hand certain sus- 
 pensions are often settled within a few hours. 
 
 (c). Protective effects against weathering. 
 
 If a colloidal solution of tri-calcium arsenate could be 
 used, it would not only have an increased toxicity, but it would 
 also tend to gelatinize on the foliage of the plant on which it 
 
4. 
 
 is sprayed. This gelatinous form would not be so easily washed 
 off by the rain and would therefore materially reduce the num- 
 ber of sprayings necessary each year. It might be thought that 
 this gelatinous coating would cover the pores of the leaves and 
 in this way interfere with the respiration and transpiration of 
 the leaves. However, sprays are not often applied so heavily 
 but what the liquid collects in tiny droplets instead of form- 
 ing a solid coating. 
 
 Ill . 
 
 Experimental, 
 
 (a). Preparation of the colloid. 
 
 A calculated amount of KOH solution was added to a solu- 
 tion of KH 2 AsO^ to form K^AsO^ solution. This solution was fil- 
 tered and diluted to 3N, A solution of GaOlg was made up, fil- 
 tered, and diluted to N. 
 
 Five cc. of the 3N potassium arsenate solution were dil- 
 uted to 500 cc. and 15 cc. of the N. calcium chloride solution 
 were diluted to 500 cc. Seventeen g. of gelatin were added to 
 the calcium chloride solution and with both solutions near boil- 
 ing, the arsenate solution was added slowly to the calcium chlor- 
 ide and gelatin solution. The stirring was continued for a few 
 moments after the KjAsO^ solution had been added. This gave a 
 solution or suspension which was white by reflected light and 
 yellowish color by transmitted light. This solution gelatinized 
 after standing about 20 hours. When diluted with two parts of 
 water, it gave a clear, water white solution, which did not ’gel- 
 atinize and which remained clear for several days . An increased 
 
5 . 
 
 amount of gelatin made a more viscous jelly. When the solutions 
 were heated to about the melting point of gelatin ( 40 ® G.), in- 
 stead of 100 ® G. the product appeared to be the same as was ob- 
 tained in the other case. Ga(N03)2 was tried in place of the 
 GaGl2 but the jelly did not seem to remain viscous quite as well. 
 
 An attempt was also made to make the colloidal Ga3(As04)2 
 by dropping H^asO^ into a paste of Ga(0H)2 similar to the method 
 recommended by Reedy and Haag (l). The gelatin was dissolved in 
 the arsenic acid. This method proved unsuccessful because the 
 gelatin seemed to slow the reaction too much. Even when the so- 
 lution was made distinctly acid (phenolphthalein ) , by the time 
 the upper part of the solution had gelatinized, the lower part 
 would be decidedly colored, showing that the OH ions were again 
 in excess . It was thought at first that this formation of OH 
 ions indicated that hydrolysis was taking place but the fact 
 that only a fraction of the calculated amount of arsenic acid 
 was necessary to make the solution acid seems to show rather 
 conclusively that it was the slowness of the reaction which 
 caused the phenomena. 
 
 The above concentrations give a 0.015 H solution of Ga^- 
 (As 0^)2 or 0.995 g. of tri-calcium arsenate per liter. 
 
 (b). Preparation of other arsenates. 
 
 Galculated amounts of the K^AsO^ solution were added to 
 solutions of AgNOs, Pb (1103)2, and Gu(N03)2 to form Ag3As04, 
 Pb3(As04)2, and Gu3(As04)2 respectively. In each case the prod- 
 uct was filtered, thoroughly washed, and then dried on a clay 
 plate. Each product was kept in a stoppered sample bottle. 
 

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6 • 
 
 (c). Determination of the solubilities 
 of the arsenates . 
 
 The solubilities of the arsenates were determined by meas- 
 uring their electromotive forces, when used as ’half cells with 
 silver electrodes, and then calculating the ion concentrations 
 from 'the equation: 
 
 E = 0.0585 log G’/C" 
 
 The half cells (used against N/10 Gal.) were: 
 
 Ag/AgjAsO^/SN Kl'iOj 
 Ag/aggAsO^/Pb^ (AsO^ )2/3N KiJOj 
 Ag/Ag^AsO^/GuglAsO^)^^^ KHO^ 
 
 Ag/Agj^AsO^/Gol. Ga5(AsO^)g/3N KNO^ 
 
 The setup used was the ordinary one consisting of a stor- 
 age battery, potentiometer box, variable resistance, galvanom- 
 eter, and standard cell. 
 
 Gonsidering E’ as the potentiometer reading and using a 
 N/io AgGl cell as a reference, the above equation becomes: 
 
 E' - .0474 r .0585 log G (AgCl )/C ( Ag 3 As 04 ) 
 
 z .0585 log(A^)AgGl - ^0585 log (A^)Ag'^As 04 
 The concentration of Ag ions in n/ 10 AgGl is 1.94 x lO”*^ 
 and after substituting this value in the equation, it becomes: 
 
 E’ - .0474 « .0585 log 1.94 x 10”^ - .0585 log (Aj)Ag 3 As 04 
 E’ : .0474 + .0585 log 1.94 x 10"^' - .0585 log (Ag)Ag^AsO^ 
 Whitby ( 4 ) found that the solubility of Ag^As 04 was 
 8.5 X 10“^ g. per 100 g. of solution. This is equal to 8.5 x 
 10"^ g. per liter of solution. 
 
 Ghanging this to moles it becom.es: 
 

7 
 
 8.5 X 10"^/462,6 = 1.839 x 10“5 = (ASO 4 ) 
 
 1.839 X 10-3 X 3 = 5.517 x 10“5 = {A$) 
 
 Hence : 
 
 (Ag)^ X (Aio”) r (5.517 X 10“^)^ x (1.839 x 10 - 5 ) 
 
 : 308 X 10-20 
 
 Therefore: 
 
 (Ag) r 308 X 10“^ V (AsO^) 
 
 Substituting, the equation becomes: 
 
 E’ = .0474 + .0585 log 1.94 x 10 -S --.0585 x 
 log 308 X 10-20/ (ASO4) 
 
 E’ = ,0474 + .0585 log 1.94 x 10“- - .0585 x log 
 
 308 X 10"^^ + .0585 log (ASO 4 ) 
 
 Combining the terms which are constant for this work, the 
 
 equation becomes : 
 
 E' = constant -** .0585 log (As5”) 
 
 = 0.67905 + 0.0585 log (ASO 4 ) 
 
 Log (AsOJ) = (E» - 0.67905.) 
 
 0.0585 
 
 The following readings were made: 
 
 No. 1. Silver arsenate (to try and check Whitby's results). 
 No. 2 . Copper arsenate. 
 
 No. 3. Lead arsenate. 
 
 No. 4. Apiece of gelatin from a Colloidal calcium arsenate 
 solution several days old. (Made from Ca(N 03 )g). 
 
 No. 5. Some colloidal calcium arsenate which had been made 
 from calcium nitrate'} but had been diluted with tv^o parts of wa- 
 ter and therefore had never gelatinized. 
 
 The above readings were taken after the cell had been made 
 
1 
 
 1 
 
8 . 
 
 up for at least 24 hours . 
 
 No. 6. Colloidal oalcium arsenate made iiith CaCl 2 . This 
 
 reading was taken immediately after the gelatinous colloid had 
 
 been put in the cell. 
 
 No. 7. No. 6 after standing for 72 hours. 
 
 No. 8. Same as No. 6 but made with Ga(NO„Oo instead of 
 
 o ^ 
 
 G aC Ig • 
 
 No. 9. No. 8 after standing for 72 hours. 
 
 
 Results • 
 
 
 
 
 Reading 
 
 No. 
 
 Re ading 
 (Volts ; 
 
 (AsO” 
 
 ) 
 
 1. 
 
 0.1820 
 
 3.185 
 
 X 
 
 10“^ 
 
 2. 
 
 0.1828 
 
 3.295 
 
 X 
 
 10“^ 
 
 3. 
 
 0.1933 
 
 5.000 
 
 X 
 
 10"^ 
 
 4. 
 
 0.1155 
 
 2.330 
 
 X 
 
 10-10 
 
 5. 
 
 0 . 12 15 
 
 2,955 
 
 X 
 
 10-10 
 
 6. 
 
 0.0716 
 
 4.100 
 
 X 
 
 10"^^ 
 
 7. 
 
 0.0325 
 
 8.890 
 
 X 
 
 10”^^ 
 
 8. 
 
 0.1566 
 
 1.172 
 
 X 
 
 10“^ 
 
 9. 
 
 0.1425 
 
 6.720 
 
 X 
 
 10’^^ 
 
 
 IV. 
 
 
 
 
 
 Summary . 
 
 
 
 
 Calculating from the solubility given by Whitby (4), read- 
 ing NO. 1 should give the concentration of the AsO^ ions as 
 1.84 X 10”^ instead of 3.185 x 10“^. 
 
 This difference makes the accuracy of the other figures 
 rather doubtful. Even though the figures may not be quite ac- 
 curate, however, the 7 / seem to show that the copper and lead ar- 
 

 
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 senates are a little more soluble than the silver arsenate; 
 that colloidal calcium arsenate, especially when prepared with 
 GaCl2, is even more insoluble than the silver arsenate; and that 
 none of these arsenates h^T'drolyses to any appreciable extent. 
 
10 . 
 
 V. 
 
 Bibliography . 
 
 (1) . J. Ind . & iilng. Chem. 13, #11, p. 1038 (Nov. 1921) 
 
 (2) . Koll. Zeit. 28, 145-8 (1921). 
 
 (3) . Phil. Mag. U., 425 (1906). 
 
 ( 4 ) . Zeit. Anorg. Chem. 67,107 .