T H E J O U R N A L OF I h T D U S T R I A L A N D ENGINEERIATG CHEMISTRY
May, 1913
As recently pointed out by A. M. Smoot,I this lime as sulfate is not insoluble in the course of the regular wet assay of pyrites and its sulfur is estimated as available sulfur. This being so i t should rightly be included as such in the cinder, but from recently published data concerning the decomposition temperature of sulfates i t would seem as though the combustion method would not include this. The temperature given for the decomposition of CaSO, is 1 2 0 0 ~ C . a Mr. Nitchie finds t h a t CaSO, is not decomposed in his method of analyzing roasted ginc blendes. If so, the sulfur equivalent to the lime should remain in the furnace with the ferric oxide obtained b y roasting pyrites cinder. My check analyses b y gravimetric means indicate t h a t if the lime is combined with sulfur in the cinder, the combination is broken during the test and the sulfur evolved as gas. I t is probable t h a t the ferric oxide plays some part in this reaction. If, however, the lime retained its equivalent of sulfur i t would, as seen above, amount with most kinds of pyrites t o only one or two-tenths of one per cent. Two grades of Spanish pyrites with which the writer is quite familiar contain several per cent of zinc and a number of others smaller amounts. By the water test above referred it is easy t o determine t h a t some of the soluble sulfate is present in combination with zinc. What Mr. Nitchie says about zinc sulfate in roasted blende applies t o pyrites containing zinc, but the reactions may include the action of iron sulfide a n d oxide on zinc sulfate for the results indicate a complete decomposition of this last salt. DETROIT, MICH.
40 1
separation is essential. The reason for requiring a higher factor than the theoretical is believed t o be due t o the lead peroxide carrying one-half molecule of water. Solution of the spelter sample is effected by dilute hydrochloric acid according t o Oswald Gunther' or dilute sulfuric according t o Eliot and Storer, until nearly all zinc is dissolved. This procedure makes it possible to operate on a large sample and each 0.1 cc. of potassium permanganate (0.568 gram t o the liter) equals 0.001 per cent lead, when 19.2 grams spelter is taken. The insoluble l.ead, cadmium and some zinc is filtered off, washed, dissolved in nitric acid, diluted, ammonia and ammonium persulfate added t o peroxidize the lead. .After filtering, the cadmium may be precipitated in the filtrate b y hydrogen sulfide. The substitution of trichloracetic acid, according t o Fox,zfor any one of the mineral acids usually employed in separating cadmium and zinc, has been found advantageous, since it is not dissociated to the same extent as hydrochloric or sulfuric acids, and even rather concentrated solutions do not prevent the complete precipitation of cadmium. I n the case of mineral acids the strength must be kept within narrow limits, a s is well known. A slight excess prevents the complete precipitation of cadmium, while insufficient acid causes zinc also t o be precipitated, making several reprecipitations necessary. By means of trichloracetic acid usually only one re-precipitation is called for, unless it is accompanied by more zinc than was aimed a t originally in dissolving. ANALYTICAL M E T H O D
A NEW TECHNICAL METHOD O F SPELTER ANALYSISa
Weigh out r 9 . z grarm of the spelter and place in B y ERIC JOHN ERICSON No. 3 beaker. Add 2 0 0 cc. ordinary water and 43 cc. At the Sixth International Congress in Rome, 1906, concentrated hydrochloric acid (1.2 sp. gr.), or I O O cc. chemists were invited t o publish their methods of water and 50 cc. dilute sulfuric acid ( I : 3 ) ; allow spelter analysis for comparison and possible unification. t o stand over night whenever cadmium is t o be deHence I now present a scheme, involving the applica- termined; if lead alone is wanted a few hours' time tion of a n original method for lead, which, a t the same will do. Filter off metallic, consisting chiefly of time, effects a separation from cadmium. The funda- lead, cadmium and some undissolved zinc, and wash mental reactions were described in the Journal of the with hot water. Transfer whatever metallics are on American Chemical Society, September, I 904, and the filter paper back into the beaker by means of a subsequently in the Engineering and Mixing Journal, jet of water. This can be accomplished without loss July 2 j , 1908, and May 2 2 , 1909, giving its application if done a t once before the paper gets dry. Now add t o ores. It is based on the following reactions: I O cc. concentrated nitric acid and boil unaii brown Pb(XO,), 4NH40H (NH,),S,O, fumes cease t o come off. Filter and wash if traces = PbO, 2iYH4N0, 2(NH,),SO, 2H,O of tin or antimony are indicated, which is very seldom PbO, H,O, 2 H N 0 , = Pb(NO,), aH,O 0, the case. If filtered and washed the volume will jH,02 aKMnO, 6HN0, probably be large enough; if not filtered, add 1 0 0 cc. = zICNO, 2Mn(NO,), 8H,O 50, distilled water, 30 cc. concentrated ammonia and Hence: zKMnO, = 4H,O, = SPb 5-10 grams ammonium persulfate, depending on size of precipitate. Should lead be unusually high, Since the theoretical factor 5Pb = 1.851 gives too say over 1.00 per cent, it is best .to add half of the IoFe persulfate before adding the ammonia. Boil five low results, the empirical factor 1.92 was chosengiving results agreeing exactly with the standard gravi- minutes and allow ten more for the precipitate t o settle. metric method-whenever a preliminary separation Then filter while still warm through double 11 or 12.5 of lead is not necessary, and 1 . 9 5 for ores where such cm. No. I F filters. Wash four times with a hot I O per cent ammonia solution and five times with hot
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Eng. Mzn J.. 94. 412 Met. and Chem. En0 , 10, 172 Paper presented a t t h e Eighth International Congress of Applied Chemistry. S e n York, September, 1912. 2
1 Bericht der Internationalen Analysen K o m n i s s i o n an dqr V I International Kongress f u r Angewondte Chemie i n R o m , 1906, p. 5 1 . 2 Jour. Chem. Soc.. London, 1907, p. 964.
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T H E J O U R N A L OF I N D U S T R I A L A N D Eh'GIl'iEERIiVG C H E M I S T R Y
water. Transfer filter with precipitate back into same beaker in which precipitation was made. Add 2 5 cc. hydrogen peroxide solution (10-50 cc. hydrogen peroxide U. S. P. strength t o the liter, plus 5 0 cc. concentrated nitric acid). Stir until dissolved, add 15 cc. nitric acid, (1.20 sp. gr.) plus 75-100 cc. distilled water and titrate the excess of the hydrogen peroxide by standard potassium permanganate of the strength indicated above. For instance, if 2 5 cc. H,O, blank requires 80.0 cc. KMnO, and the sample 34.5 cc. then the lead equals 80.0-34.5 0.455 per cent. If 2 5 CC. of the H,O, solution should fail to dissolve the lead peroxide, add another 2 5 cc. and double the blank. The accompanying samples taken from practice, show t h a t the new method checks exactly with the long chromate method:
Vol. 5, No. 5
iron and cadmium. Zinc is taken by difference. Copper, tin and antimony are indicated and may also be determined, whenever present. The lead method is a marvel of accuracy and gives very concordant results. I n making this claim, I a m aware of recent criticism in regard to shortcomings of most analytical methods proposed. This one will be found, on investigation, to be a notable exception, and its daily use for several years has fully demonstrated its reliability. EDGARZINC Co.
ST.Lours
FACTORY METHOD FOR THE DETERMINATION O F TOTAL FATTY ACIDS IN COTTON-SEED FOOTS' B y F. N. SMALLEY
The method herein described is proposed for a rapid method for the determination of the total fatty acids Gravimetric(a) in cotton-seed foots, or soap stock, and similar maEricson method as chromate terials, by a determination of the iodin number of the Refined spelter.. . . . . . . . . . 0 , 0 5 2 per cent lead 0 . 0 5 5 per cent lead Refined spelter. . . . . . . . . . . 0.082 0.083 same, and its conversion into terms of fatty acids b y Refined spelter.. ......... 0 . 0 4 3 0.044 means of a n appropriate factor. Prime Western spelter.. . . 0.530 0.538 Cottonseed oil soap stock is the sludge removed Prime Western spelter.. . . 0.533 0.531 from crude oil in the process of refining with caustic Special spelter.. ......... 1.279 soda, and consists of the soda soaps of the fatty acids ( a ) Filitz, Praktische Leitfaden f u r Zinkhutien-laboratorien, p. 2 7 . of the oil, together with some neutral oil, coloring and For spelter rather high in lead, it will be advisable albuminous matters which are characteristic of crude t o check the lead factor against a standard spelter, oil, caustic soda and water. under identical conditions. The most accurate method of the determination of the total fatty acids is the Official Method of the CAD,MIUM D E T E R M I K A T I O N Interstate Cotton-seed Crushers Association, which Boil the ammoniacal filtrate from lead until nearly consists in complete saponification of the fat by means neutral and a white precipitate appears, then take of alcoholic soda, evaporation of the alcohol, solution off hot plate and add 40 cc. dilute sulfuric acid ( I : 3) of the soap in the hot water, decomposition of the soap and boil about ten minutes. Add water t o make the with dilute mineral acids, melting of the liberated volume about z o o cc. and saturate with hydrogen f a t t y acids, chilling to form a cake, filtering and washsulfide gas, adding a little water occasi'onally. Allow ing free from mineral acid, extraction of the cake the precipitate t o settle, filter through double filters with warm petrolic ether, evaporation of the solvent and wash a few times'with water. Redissolve on the and weighing of the residual fatty acids. filter the cadmium sulfide contaminated with zinc The method is so long t h a t i t is almost useless for sulfide, in as little warm dilute hydrochloric acid as factory control, and for that reason after trials of a possible and wash with warm water. If copper is number of various proposed methods, the iodin present, the sulfide remains insoluble on the filter. method was selected in the summer of 1905, as the best I t may be ignited and weighed as CuO or colorimetric- ,fitted t o obtain the most accurate results in the shortest ally. time. Since then i t has been in continuous use in the The filtrate containing the chlorides of cadmium refineries of the Southern Cotton Oil Company. and zinc is nearly neutralized with dilute ammonia The method is carried out as follows: After the and about 8 grams of trichloracetic acid dissolved in sample has been well mixed, weigh out accurately water added, or enough t o dissolve the CdS formed by 0.5 gram on t o a small square of fat-free paper. This neutralization. Add distilled water t o about 2 0 0 cc. is then introduced into a ground glass stoppered bottle volume and reprecipitate Cd by H,S. Allow t o settle, with neck so arranged t h a t the joint can be sealed filter and determine by any of the usual methods, with the potassium iodid solution. Five cc. of carbon preferably as sulfate or phosphate. Duplicate de- tetrachloride and 2 0 cc. of Wijs' iodin solution are terminations usually agree within a few hundredths of added. The bottle is stoppered and the contents I per cent. gently shaken until the soap stock is in solution. Iron is determined in a separate sample by dissolving Seal with potassium iodid solution and allow to I O grams in 75 cc. dilute sulfuric acid and allowing it to stand for thirty minutes. stand until practically all dissolved; a few drops The determination of the iodin number is now of platinic chloride added t o effect complete solution; carried out in the usual Wijs' method, and the rethen titrate with the same standard permanganate sultant number is converted by division by 1.24 into solution used for lead. Each 0.1 cc. KMnO, solution per cent fatty acids. equals 0.001 per cent. iron on a Io-gram sample basis. The factor was arrived at by comparison of the The method outlined above takes care of the usual 1 Paper presented a t the Eighth International Congress of Applied constituents called for in spelter analysis, such as lead, Chemistry, New York, September, 1912.
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