January, 1929
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Solid Solutions of Lime and Arsenic Acid’ A. T. Clifford and F. K. Cameron UNIVERSITY OF KORTH
CAROLINA,
CHAPELHILL,N. C.
Another series of bottles of 250 cc. capacity was prepared MITH2 has shown that in the system calcium oxide, arsenic acid, and water a t 25” C., monocalcium arsenate, but with concentrations of arsenic acid sufficient to insure CaH4(As0&, is the stable solid phase in contact with precipitation of calcium diarsenate as solid phase. Fifty liquid solutions containing more than 518 grams arsenic cubic centimeter portions of the mother liquor were withoxide, AS&, per liter, while a diarsenate, CaHAsOa.HZ0, drawn for analysis. is the stable solid in contact with more dilute liquid solutions, Calcium was determined by adding sufficient nitric acid down to a concentration of 25 grams arsenic oxide per liter. to insure complete solution. Then, after neutralizing with At yet lower concentrations of the liquid phase a more basic ammonia slightly acidified with acetic acid, ammonium solid is stable, and it appears that this has generally been oxalate was added. The precipitated calcium oxalate was regarded as a mechanical mixture of calcium hydroxide or taken up with sulfuric acid and the mixture titrated with calcium oxide with a hypothetical tricalcium a r ~ e n a t e . ~standard solution of permanganate. Arsenic in the liquid That the latter exists cannot be assumed on the basis of the phase was precipitated as silver arsenate from solutions evidence so far offered; while the existence of a series of slightly acid from acetic acid. The silver arsenate, after solid solutions of calcium oxide and phosphoric acid in con- washing, was dissolved in nitric acid and the silver precipitact with solutions of low concentration of phosphoric acid, tated and weighed as silver chloride. Arsenic in the solids as shown by Cameron and Bell,4 suggested that a similar was determined by bringing the solid into solution with nitric series of solid solutions of calcium oxide and arsenic acid would acid, adding potassium iodide, and then strongly acidifying be found to be stable in contact with liquid solutions of with hydrochloric acid. The liberated iodine was titrated arsenic acid. It is probable that the calcium arsenates of with a standard solution of thiosulfate. Blanks showed the commerce, now widely used as insecticides and in combating effect of the nitric acid used to be negligible. The amounts weevil infestations, are such solid solutions. They are some- of arsenic in solutions 1, 2, and 3 were too small to be detertimes precipitated a t considerably higher temperatures than mined by the method described. It was shown to be present 25” C. and may not be in final equilibrium with their mother by the Reinsch test. liquor, since the attaining of such equilibrium has been found Discussion of Results to be a matter of weeks or months rather than hours. But the writers know of no evidence that they are different in any The results obtained are given in Table I. The data for essential from the precipitates they studied. solutions 8 and 10 in contact with dicalcium arsenate are in Experimental good accord with those of Smith. The data for solution 9 The lime and the arsenic acid used were C. P. grade obtained are taken from Smith’s papera2 from the Baker Chemical Company. The arsenic acid was shown to be free from arsenious acid on testing with iodine Table I-Concentrations in t h e System CaO-Asz03-HzO at 25* C. and starch paste. LIQUIDPHASE SOLID PHASE SOLUTION ,4 series of Winchester quart or acid bottles were nearly Ratio AszOs: CaO As206 CaO filled with a saturated solution of calcium hydroxide, and Grams per 1000 grams solulion varying quantities of a solution of arsenic acid (250 grams 1.083 AszOa per liter) were added to the several bottles with con1.117 1.213 tinued stirring. A fluffy, non-crystalline precipitate formed 1.364 in each case. Six of these bottles, occasionally shaken, were 1.414 1.569 kept for 2 months in a large water bath a t approximately 25” C. Because of the low concentrations in the liquid phase and the analytical difficulties involved, the standard “indirect” methods of analysis could not be reliably employed and the procedure followed was to determine the ratio of AszOs to The ratio AszOj to CaO for the solid phases in contact CaO in the solid phases. The solid phases were separated from the mother liquors by centrifuging, the very small Kith solutions 1, 2, 3, 4, 5, and 6 varies continuously from amount of mother liquor remaining being negligible since 1.08 to 1.60. Consequently, these solids are members of a very dilute. One-liter portions of the mother liquor were series of solid solutions. The ratio of arsenic acid to lime in withdrawn from the bottles through cotton-wool plugs in the hypothetical tricalcium arsenate is 1.367, corresponding such a way as to prevent absorption of carbon dioxide in the to a solution near No. 4 in the series tested. If this salt operation. Solutions 1, 2, and 3 were basic to phenolphthal- actually exists, we then have two series of solid solutions inein. Solutions 4 and 5 gave no color reaction with either tersecting, instead of one series. The analytical methods phenolphthalein or methyl orange. The other solutions available are not sufficiently delicate to determine which alternative is correct. A plot of these results shows that the were plainly acid in reaction. isotherm for the liquid solutions in contact with the solid Received June 28, 1928. solutions has a minimum point. There can be, therefore, a J . Am. Chem. Soc., 43, 259 (1920). liquid solution in equilibrium with a solid solution in which $Robinson, J . Agr. Research, 13, 281 (1918); Hapwood and Smith, U. S. Dept. Agr., Bull. 760 (1918); Tartar, Wood, and Hunter, J . Am. the arsenic acid-lime ratio in the liquid phase is the same as Chem. Soc., 4 6 , 804 (1924); McDonnell, Smith, and Coad, U. S. Dept. Agr., in the solid phase. The plot indicates that it probably lies Bull. 1116 (1922); Smith and Hendricks, IWD. EWG.CHEM.,16, 950 (1924); very close to the point where the solid phase has the ratio Reedy and Haag, I b t d . , 13, 1038 (1921). ‘ J . Am. Chem. Soc., 37, 1512 (1905). corresponding to tricalcium arsenate. Continued leaching
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I N D U S T R I A L A N D ENGINEERING CHEMISTRY
of this complex will give solutions with a constant ratio of arsenic acid to lime, which has misled previous investigators to consider the complex a definite compound. There seems to be no evidence that tricalcium arsenate can be formed from aqueous solutions, nor persist in contact with them. Analytical methods purporting to separate it from other calcium compounds should be riewed with caution.
Vol. 21, No. 1
Tricalcium arsenate may be formed, as in the Cullen process, where calcium oxide and arsenic trioxide are heated in a current of air. As far as the writers know, the products so obtained are not crystalline, and one may well hesitate to express a positive opinion. That any one of them will, in contact with water, form two solutions, one solid, the other liquid, is reasonably certain.
Deterioration of Soap-Nicotine Preparations-11’ C. C. McDonnell and J. J. T. Graham FOOD,DRUG,AND INSECTICIDE ADMINISTRATION, U. S. DEPARTMENT OF AGRICULTURE, WASHINGTON, D. C.
N OUR work in connec-
Commercial soap-nicotine preparations decrease kettle and heated somewhat in nicotine content on storage. This loss is shown to tion with the e n f o r c e below looo C. until the soap merit of the Insecticide be due to volatilization of nicotine and, in the case of attained a pasty consistency, Act it has been found that soaps made from drying oils such as fish oil, to oxidation when it was transferred to a most of the commercial soap which results in a condensation product between the shallow, flat, enameled pan preparations containing niconicotine and the fatty acids. The work here reported to cool. Small quantities of tine, especially those in cake shows that this decomposition can be prevented by water and nicotine were lost form, contain less n i c o t i n e packing the soaps S O that they are completely protected d u r i n g saponification, but t h a n t h e manufacturer from the air and that such products can be produced c o m p l e t e a n a l y s e s of the and marketed S O as to retain their nicotine content for finished soaps were made, claimed to be present. Sevat least two years. Fish-oil soaps were used in era1 years ago an investigamost of the work. They were tion to determine the cause of this shortage was begun. I n a previous paper McDonnell prepared in three types-neutral, alkaline, and superfatted and Nealon2 reported that hard soaps made from sodium hy- soda soaps (both in cake and paste form), and neutral and droxide, menhaden fish oil and nicotine solution lose nicotine alkaline potash (soft) soaps. The cottonseed oil, red oil, rapidly on storage regardless of the type of package, and that and stearic acid soaps were prepared only in the neutral form. potash soaps (soft soap) and soft soda soaps containing nico- The formulas are given in Table I. tine retain practically their original nicotine strength for a Soft soda soaps were prepared from portions of the hard period of four years. I n other words, whether or not nicotine soaps A, B, C, I, and K by adding a sufficient quantity of is lost depends upon the physical condition of the product. water to convert them to the consistency of a thin jelly and It was further reported that any loss of nicotine was due, not then enough nicotine solution to make the total nicotine to volatilization, but t o chemical changes, whereby it was content approximately 3 to 4 per cent. These were desigconverted into an insoluble, non-volatile, polymeric form nated D, E, F, J, and L. All the samples were packed in or a condensation product, probably the latter, as the de- glass jars fitted with rubber rings and tightly closed. The crease in nicotine was accompanied by a decrease in the hard soaps were cut into cakes about 4 X 4 X 10 cm. and fatty acids of the soap, indicating a reaction between the two. wrapped in heavy waxed paper before being placed in jars. The present paper reports the results of additional work A sufficient number of cakes was prepared so that a fresh on this subject, including that with soaps made from different cake could be taken for each analysis, and all samples were analyzed a t the time of packing and after storage for 1, 3, types of oils, both drying and non-drying. 5, 8, 12, and 24 months.
I
Preparation of Samples
Soda and potash soaps were prepared with the follotving oils and fatty acids: menhaden fish oil, cottonseed oil, linseed oil, red oil, and stearic acid. Nicotine was added in the form of a water solution of the ‘‘free” alkaloid. Note-Soaps containing nicotine sulfate solution, which is the most common form of commercial nicotine preparations, would no doubt act in the same way. Since alkali or soap sets nicotine free from nicotine sulfate, its use would have liberated fatty acids and added an additional factor in making i t necessary t o provide for more alkali in order t o produce a neutral soap.
The saponification values of the oils and fatty acids were determined, and the exact amount of alkali solution (prepared practically free from carbonate) required to form a neutral alkaline or superfatted soap as desired was added. Saponification was accomplished in a jacketed steam kettle equipped with an agitator, the ingredients being added to the hot 1 Presented as a part of the Symposium on Insecticides and Fungicides before the Division of Agricultural and Food Chemistry a t the 75th Meeting of the American Chemical Society, St. Louis, Mo., April 16 to 19,
Methods of Analysis
In order to secure a representative sample, a section through the center of the cake of the hard soaps was taken in each case, and the soft soaps ere thoroughly mixed and a pertion was removed for analysis. W a ~ ~ ~ - W a t ewas r determined by distilling 15 to 20 grams Of the With 50 Of dry (about lo grams Of lump rosin being added to prevent foaming) and the distillate was collected in a distilling tube and measured, according to the method described b i Dean and Stark.3 ’ FATTY Acms-For the determination of fatty anhydrides, nicotine, and insoluble material, a weighed sample of approximately 20 grams was dissolved in hot water and transferred to a separatory funnel and an excess of hydrochloric acid was added. After the solution was cool the fatty acids were extracted with ether, the ether was evaporated in a weighed beaker and the residual fatty acids were weighed. The residue in the separatory funnel was dissolved in alcohol and transferred to a weighed beaker. The alcohol was
1928. 2
IND. ENG.CHEM.,16, 819 (1924).
a
J. IND. ENG.CHEM, 12, 486 (1920).
