CLAY ANALYSIS
I 603
zinc; the mean of the only rapid analyses of solution A where the precipitation was complete (Nos. I , 3 and 5, Table 4) is 0.1983 g. I n the case of the other solutions ( B and C) the mean of all the determinations where complete precipitation was assured (except Nos. 5 and 8, Table 5 ) , .was assumed to be the correct value and the error calculated on this basis. T h e deposit was generally of a fine steel-gray color and metallic luster. I t was noticed that the character of the precipitate is very dependent on the surface of the cathode; on one cathode which had been treated for a long time with acids and thus had its surface roughened, the precipitate was always of a dark color and had a tendency to oxidize, as shown by experiments 5 and 8 (Table 5 ) , where this cathode was used.
Summary. I . With electromagnetic rotation of the electrolyte 0.1 g . zinc can be completely precipitated by 4.5 amperes in 30 minutes on a nickel gauze cathode. About 8 g. of sodium hydroxide should be used, and the electrolysis should be conducted at as low a temperatue as possible. 2 . For quantities of zinc up to 0.2 g. the current-strength should be 4-5 amperes for 15 minutes and then about 1.5 amperes for 2 0 minutes. (Other conditions are the same as in I ) . 3. T h e testing of the liquid remaining after electrolysis is essential. 4. I t is highly improbable that complete precipitation of 0 . 2 g. zinc can be obtained with 5 amperes in 1 5 - 2 0 minutes, as stated by Exner and Ingham. From the results obtained it would also seem improbable that the concordant results obtained by Miss Langness with 10-13 amperes in 3 minutes represent complete precipitation. T h e work on which this and the preceding articles are based was done during the spring and summer of 1907 in the electro-chemical laboratory of the Royal Technical High School at Berlin. I take this occasion to thank Professors von Knorre and Peters, and Dr. Arndt, of that laboratory, for their interest in this work and the many kindnesses shown me duriug its course. UNIVERSITY O F MINNESOTA,
Minneapolis, hlinn., Aug. 2 0 , 1907.
CLAY ANALYSIS-AN EXAMINATION OF THE RESIDUE LEFT AFTER VOLATILIZATION OF THE SEPARATED SILICA WITH HYDROFLUORIC AND SULPHURIC ACIDS. First Paper. B Y W.
R. B L O O R .
Received August 5 , 1907.
I t has been generally assiimed that the residue left after volatilization of the separated silica with hydrofluoric and sulphuric acids in the ordinary process of clay analysis is composed of iron and aluminium oxides and as such is to be added in with them.
I 604
W . R . BLOOR
With the view of testing the correctness of this assumption, an exaniination was made of a number of these residues, obtained in the course of a series of analyses of clays of the State of V7ashington. The method used in separating the silica w a s that outlined in Bulletins 176 and 305, I-.S. Geol. Survey, special precautions being taken to eiisure complete used fusioii. From 6-8g. of sodiuiii cru-bonatc: per gram of c l a ~were and the fnsioii w a s continued with frequent rotation of the crucible for fifteen minutes after the melt was quiesceiit. T h e silica was obtained by double evaporation ( t o approxiiiin!e dryness except i n S o s . I , 5, 7 and I o . Xvliich were allowed to d r y for t h e e hours at 1 2 5 " ) ~with intervening filtration. ant1 ~vashetl uiitil the washings gave 110 cloudiness with sill-er nitrate solutioii. After blasting to wiistaiit weight, it \vas moistelled with water ant1 .;:ilphuric acid a n d \-olatilized Ivitli hJ.tlrofluoric acid. T h e lveiglied residue \\-a$ f u d with potassinni hisulphate and takeii up with water aiitl a little sulpliuric acid. Any residue \vas filtered off and weiglirtl a s insoluble matter. Fc,O, and A1,0,, etc., were tietermiiied i l l the usu:il i i i m i i t ~ i - . CaO was olitaiited by double precipitation. T h e first prccipitatioii was geiiernlly slow a n d w:is allowed a d a y or 50 to coiiipletc. T h e precipitatct \vas filtered off, dissolved ' in dilute h\.drochloric acid ant1 reprccipitated. the second precipit a t 1011 ta.kiiig place iiiimetliatcly. hIg0 \vas obtained as iisual. TiO, was found in all cases \\-here it was prcseiit in the c l n ~ - .b u t \vas not tletermined. Blanks were ruii for all reaxelits. All the samples nientioried i i i tlic following table were ordinary clays with the exception of Sos. I O arid I I , nrhicli were argillaceous limestones. T h e average conipositioii of the residue as drawn froiii the accompaxiying table is: Fe,O,,, A1,0,,, ctc., (precipitable 1)y ammonia in presence of arnnioniuni salt) 5'7.36%: CaO, 21.487h: MgO, 14.05%. T h e residue averages I . O I $ of the separated silica. In Kos. 1 % 5, 7 and 10 the mass was allowed to dry for three hours on a hot plate at 125' with t h e result that while there was an increase in the total residue of about 40$, the amount of Fe,O, arid A1,0, was increased only about 7 %. Later experiments also go to show that drying at this temperature does not materially increase the amount of Fe,O, and A1,0, in the residue. When the residue compared with the silica is large (Nos. I , 2 , 3, 5, 7 , I O and I I ) the percentage of Fe,O, and A1,0, present, is larger, but not markedly so (increase of 4% %). When the per cent. of CaO is high in the original sample (Nos. 3, 4, 8, g , I O , 1 1 , 13, 14, 16, 1 7 . 2 0 , 2 1 and 22-averaging 2.01%) the percentage of Fe,O, and A1,0, in the residue is lower (decrease of 4 % ) , while the percentage of CaO is somewhat higher (7% increase), than the average.
CLAY *%NAI.YSIS
I 606
S. t V . I’.iRR
Taking the results as a whole a i d iii spite of the fact that the qiiaiitity of material in each case is small, atid the liability to crror, coiiseqiieiitly great, the average results show a suprising constaiicy and justify tile conclusion that in the analysis of claj- by the inctliod outlined above, the silica 50 separated is contaiiiiriated to some degree 1)). the iiiaiii constituents of the c h \ - . T h e :uiiouiit of contaminatioii h y substances other than Fe,O, and A1,0, is howevcr, except in cxtreine cases. so small that it may be neglected unless extreme accuracy is required. Iir. F.Hillebrand’ states as follows: “Quite as rarely (as barium) is calcium or magnesiuiii ever a component of the residue, if t h e deconiposition of the rock powder n’as complete at the outset.” Since the results obtaiiied differ alniost entirely from this statement, it was thought well to coiisider some of t h e possibilities of error in the experiment. T h e main ones may be summed up as follows: ( I ! insufficient washing of the separated silica; ( 2 ) incomplete decomposition of the clay at the outset; ( 3) evaporation in porcelain may have induced containiiiation: (+) different actioii of clay and rock powder in fusion or subsequent treatmeiit. T h e first two may be dismissed as following i n the main the general usage in silicate analysis. The third possibility was made the subject of a second series of experiments. A sample of ordinary clay was taken and prepared very carefully. After fusion iii the regular way duplicate samples were evaporated in porcelain (Royal Berlin) and in platinum dishes, the silica volatilized and the residues analyzed as before. T h e results as yet are not sufficiently definite to throw any light on the point in question. PI.LL>IAS, \VhSH.
THE CONSTANTS AND VARIABLES OF THE PARR CALORIMETER. I:Y S . \V PARR. Received Jiily j,1907,
T h e calorimeter using sodium peroxide as a medium of combustion was first described in the October number of this Journal’, 1900. The chief element in the process as outlined at that time was the establishment of the ratio between the true heat of combustion of the fuel used and the total heat of t h e reaction developed by the process. For example, if the total indicated heat of a hydrocarbon, burning in a closed chamber by means of sodium peroxide were found to be 10,000 calories, then the true heat of combustion would be 7300 calories, and the other 2 7 0 0 units would represent the heat of combination of the carbon dioxide and water with the chemical employed. T h e constant, therefore, representing the part of the reaction which was to be credited to combustion, was 7 3 per cent. This factor was determined empirically Bull., 305, U. S. Geol. Survey, 80. Journal, 2 2 , 646.
* This
