July, I913
T H E -JOUR!VAL OF I - V D U S T R I A L A N D ENGINEERI,VG C H E M I S T R Y
a crystal was coated n-ith dark brown and flakes of gold were plainly discernible. S U M M AR S
If we suppose manganese tetrachloride t o be a n intermediate product, present only in very minute traces, we may find in it some basis of explanation. Suppose zAuCI, 3MnC1, J _ ZAU 3MnC1, Since tetravalent manganese is a n exceedingly weak base it should be little ionized, but it may be subject t o two other sorts of dissociations, namely: I . A molecular dissociation, MnC1, = MnC1, C1, 2 . Hydrolyt’c dissociation, MnC1, 4H,O = Mn(OH), 4HCl Theoretically we should have the hydrolysis constant Mn(OH),____ X (HC1)4 -- K MnC1, assuming hydrolysis according t o the above equation. It is obvious that the presence of acid would tend to cut down the hydrolysis and allow the tetrachloride t o become sufficiently concentrated t o make its molecular dissociation appreciable-the greater the concentration of acid the greater this tendency-and we may, in this way, easily obtain conditions under which free chlorine is liberated, as in the chlorination process. I f , however, the acid concentration is reduced below a certain figure the concendation of the tetrahydroxide will reach saturation. Any further reduction of acidity must result in the precipitation of the hydrated dioxide. I t will be seen that such a n adjustment may be very delicate indeed-and this seems to be supported b y the lack of success in preparing the tetrachloride, subject, as it would be, t o both hydrolytic and molecular dissociation.
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DEPARTMENT OF GEOLOGS UNIVERSITY OF CHICAGO
SOLUBLE ARSENIC IN MIXTURES OF LEAD ARSENATE AND SOAP1 B y H. Y. TARTARA N D L. A. BUNDY Received April 7 , 1913
There has been some complaint from horticulturists t h a t some difficulty was experienced in keeping arsenate of lead in suspension in water while spraying. I t is claimed that the lead arsenate settles out too quickly and it is difficult t o keep it stirred up. This seems t o be especially true when knapsack sprayers are used. Parker* has suggested t h a t a soap solution might be used t o aid in keeping the arsenate of lead in suspension. Parker reported results of laboratory experiments which indicate t h a t a soap solution keeps the arsenate of lead in suspension much better than water. He has also stated that the soap would be of value in causing the spray to spread more evenly over the surface of the leaves and, in midsummer spraying, the smooth skin of the apple. Mr. W. H. Lawrence, Fruit Inspector of Hood River County, Oregon, advised the orchardists in Paper presented at the Milwaukee meeting of the -4merican Chemical Society, March, 1913. Montana 9 g r . Exp. Sta., Bull. 86.
56 I
t h a t locality to try the lead arsenate-soap mixture experimentally. The results of the experiments tried indicated that in some instances considerable injury was caused to the foliage of the trees. It was suggested that this foliage injury, which resulted apparently from the use of the spray, might be due to soluble arsenic compounds formed by the reaction of the soap with the lead arsenate. Consequently, some laboratory experiments were undertaken to ascertain the amount of soluble arsenic in mixtures of soap with the different lead arsenates. While there has never been any extensive use of the lead-arsenate soap mixture, the results obtained are of special interest in showing differences in the behavior of the arsenates. Three samples of commercial lead arsenate were selected for the experiments. A brand which gave no test for acid arsenate (PbHAsO,) u-hen tried by Volck’s test’ was selected as a neutral (ortho) arsenate of lead [Pb,(AsO,),]. The other two brands were composed mostly of the acid arsenate of lead. The results of the analyses of the three brands were a s follows: Sample Neutral arsenate Per cent Moisture.. . . . . . . . , , . . . . , . . . . . 4 9 . 5 1 Total arsenic oxide (A%Oa). . . . . . 10.98 . . . .. 0.14 Soluble arsenic oxide Total lead oxide (PbO)., , . . . . . , 3 7 . 0 1 Water-soluble impurities other than arsenic oxide. . . , . , . . . . . . . . . . 1 . 0 1
.
.
. . .
Sample Acid arsenate No. 1 Per cent 47.82 15.00 0 39 33 92 0.88
Sample Acid arsenate No. 2 Per cent 47.39 16.73 0.28
33.48 0 72
Three kinds of soap m-ere used: “Ivory.” whale oil, and ordinary yellow laundry soap. The “ I v o r y ” and the whale oil soaps did not contain any free alkali, while the yellow laundry soap contained a small amount. The proportions of lead arsenate, soap and water which were used corresponded t o those recommended for use in actual spraying practice. In each of the tests, 4 . 8 grams of lead arsenate, 4 . 8 grams of soap and I liter of water were used. Each sample of arsenate of lead was tried with each of the different soaps. I n each instance, the soap was dissolved in about 500 cc. of water, the lead arsenate, after i t had been worked up with a little water, was then added and the whole made to 1000 cc. volume. The mixtures were let stand for six hours with a n occasional shaking and then filtered. The filtrates were then analyzed for their content of arsenic oxide. The determination of arsenic oxide was made by first digesting the solution with arsenic-free sulfuric acid and potassium sulfate until the solution was clear. The solution thus obtained was neutralized with sodium bicarbonate and titrated with standard iodine solution in the manner used in the modified Gooch and Browning method.’ Great difficulty was encountered in filtering the solutions for the arsenic determinations. They filtered very slowly and it was found that a small amount of lead passed through into the filtrates. 1
Science, New Series, 33. 866 (1911).
2
Bureau of Chem., Bull. 107, Revised, p . 239.
562
T H E J O U R N A L OF I.Z;D U S T R I A L A1VD E.YGI,VEERING C H E M I S T R Y
It was difficult t o ascertain if the lead was actually in solution or merely in suspension and t o make the calculations for the amount of soluble arsenic on the safest basis, the lead was determined in the usual manner’ and the amount of arsenic necessary to combine with the lead present was deducted from the total amount of arsenic found. The results obtained in this way are given in the following table: SOLUBLEARSENICIN MIXTURESOF LEAD ARSENATEA X D SOAP Grams of soluble arsenic oxide (AszOn) Material used Neutral (ortho) arsenate “Ivory” soap.. . trace Neutral (ortho) arsenate whale oil soap.. . . 0 , 0 0 4 Neutral (ortho) arsenate laundry soap. . . trace Acid arsenate No. 1 “Ivory” soap. . . . . 0.173 0,164 Acid arsenate No. 1 whale oil soap.. Acid arsenate No. 1 laundry soap. . . 0,184 Acid arsenate No. 2 “Ivory” soap. . . 0.367 Acid arsenate No. 2 whale oil soap.. . . . . . 0 . 2 8 0 Acid arsenate No. 2 laundry soap . . 0.368
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.. . .. . .. . . .. . . .. . .
Grams of arsenic oxide in lead arsenate used 0.52; 0.527 0 . 5 27 0.720
0.720 0.720 0.803
0.803 0.803
Per cent of the arsenic oxide made soluble 0 00 0 .76 0.00
24.02 22.77 25.55
45.70 34.86 45.82
These results show that in the mixtures of the soaps with the acid arsenates large amounts of arsenic are rendered soluble. The results also indicate that when a neutral (ortho) arsenate of lead is used with soap only a very small amount of arsenic is made soluble. Evidently, the use of a mixture of soap with a n acid arsenate of lead for spraying purposes would be a dangerous practice, for the amount of soluble arsenic would be sufficient t o badly burn the foliage of fruit trees. CHEMICAL LABORATORY AGRICULTURAL EXPERIMENT STATIOS CORVALLIS, OREGON
MINERALOGICAL SOIL ANALYSIS B y W M . J. MCCAUGHEY Received March 2 5 . 1913
The problem of soil fertility and sustained crop production is. a difficult one and, as Cameronz has pointed out, is a function of many variable factors, all of which are dependent upon each other. The importance of the chemical composition of a soil was recognized b y Liebig and since then many analyses of soils have been made for the purpose of indicating the soil fertility. To explain anomalous cases i t became necessary t o assume that these elements exist in the soil in combinations which are available or non-available to growing plants, and many methods of analysis were proposed and used in determining the amount of these elements available. Such methods, however, are arbitrary and add little t o our knowledge of the actual composition of a soil. The greater part of a soil consists of the residuum from rock disintegration and is composed largely of the minerals constituting the original rock and secondary mineral development due t o the alteration of the original minerals of the rock mass. This is more or less modified by geological agencies which bring about the transportation of some of the minerals and the admixture of still other material. I t has 1 2
Bureau of Chem., Bull. 107, Revised, p. 239. “The Soil Solution,” Easton, Pa. (1911).
Vol. j, S o . 7
been the experience of practical soil men that too little is known of the actual composition of soils. A soil examination consists usually in the mechanical analysis which tells only the composition in terms of the size of the soil grains regardless of their nature, and in the determination of the so-called plant foods which are soluble in constant boiling point hydrochloric acid. Very little work has been done upon the mineralogical composition of soils, though i t is obvious that differences in mineral composition will affect their physical and chemical properties. Mitscherlich has indicated that not only the size of the particles has a great influence upon the physical properties of a soil but also the shape of the particles, that is, the amount and kind of surface exposed. The recent development in the application of petrographic methods t o the study of minerals in fine powder has furnished a valuable and fruitful method for soil work. The microscopic study of minerals has been developed around and practica!ly confined t o the study of igneous and metamorphic rocks. Little work has been found in the geological literature t o indicate that such examinations have been made on soils. The most important of such examinations have been made by Sorby,* Retgers,’ Schroeder Van der Kolk3 and Delage and Lagatu.4 The chemical and mineralogical study of soil formation and of rock weathering has received more attention from geologists than pure soil work. Mineralogical compositions of wind-blown dusts have been published from time t o time. The first attempt t o systematically apply petrographic methods for the mineralogical examination of soils was made in 1889 by Steinriede. Since then little work has been done along these lines except by Delage and Laga t u . The mineralogical composition of a soil bears somewhat the same relation to the chemical analysis of a soil as the petrographic examination of a rock does to its chemical analysis. They each supplement each other. The chemical analysis does not reveal the nature of the chemical elements as they are found in the soil. The mineralogical examination on the other hand is concerned chiefly with the determination of the chemical compounds in which the elements are combined. Should more definite knowledge oE the reaction of these minerals toward water be known, a mineralogical examination would be of greater value in determining the chemical properties of a soil. An approximation t o the availability of these elements could then be known from their mineralogical combinations. Fortunately from the observation of the chemical alteration of these minerals in the soil a mineralogical examination offers, a t least, a comparative estimate of the availability of 1 “Microscopical Examination and Determination of Minerals in Sands and Clays,” Quart. J . Geol. Soc.. 1880, 5 0 . 2 “Mineral and Chemical Investigation of the Dune Sands of Holland,” .Veues Jahrb. fur. M i x . 1, 16-74 (1895). a “Mineral Composition of Holland Sands,” Der Wandelungeit der k . A k a d . von Wettenschagpen, 1896, et seq. 4 “Constitution of Montpelier Soils,” A n n . de LecoIs .Vationale de Montpelier, 4, 200-2 (1905).
