Feb., 1918
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
NazO A N D SiOz-Evaporate the filtered solution with a n excess of HzS04. Ignite and weigh the mixed sulfates and SiOz, using a tared platinum dish. After weighing take up with hot water and filter t o remove SiOz. Deduct Si02 and calculated K2S04 from the weight found for mixed sulfates and calculate the remaining Na2S04 t o NazO. METHOD F O R THE ANALYSIS O F BRINES
SPECIFLC GRAVITY-Determine with the Westphal balance. Temperature correction is 40’ F. = 0 . 0 1 0 sp. gr. The specific gravity a t 60’ F. is a n approximate indication of the per cent solids. Thus I . I O O sp. gr. indicates about I O per cent mineral solids. soLIDs-Use a pipette t o measure into a tared platinum dish a n amount of brine containing about I g. of solids. Evaporate t o dryness and fuse. Cool and weigh rapidly t o the nearest milligram. c1, A L K A L I N I T Y A N D KzO I N SOLIDS-using the same pipette as in the determination of solids, measure out the same amount of brine for the determination of C1. A similar sample is taken for alkalinity, and a third similar sample is made up t o I O O cc. and 2 0 cc. taken for the determination of KzO. The methods given on the preceding page under “Analysis of Salts” are used. From the weight of solids found the size of sample taken for t h e other determinations and the percentages found can be calculated. RECOVERY
O F ALCOHOL AND PLATINUM
ALCOHOL-Most of the platinum in the alcohol washings will be found precipitated as (“4)2PtC16 b y the NHICl in the final washings. The alcohol is decanted through paper t o separate i t from this precipitate. The filtered alcohol is then distilled on the steam bath. The residue not distilled over is treated as below for P t recovery and any platinum precipitated in the distillation flask is dissolted in aqua regia and reprecipitated with the other platinum solutions for recovery. PLATIhTUM-The contents of the Gooch crucibles containing K2PtC16 are washed into a beaker and treated with hot distilled water slightly acidified with HC1. This will dissolve the K2PtCl6, leaving t h e asbestos, which may be used again. This solution is filtered (through the filter previously used for t h e alcohol washings) into the alcohol suction flask containing the bulk of the (NH4)2PtC16. Washing the asbestos is continued until all Pt salts are in solution. This solution is then transferred t o a wide-mouth bottle, where the P t is precipitated with aluminum. A piece of aluminum rod inch diameter and about 3/4 inch long is convenient for this purpose. Precipitation is not complete until the solution is clear and colorless. I t may be necessary t o add more acid t o complete the precipitation within a reasonable time. The solution above the precipitated platinum is decanted and filtered through paper with or without suction. The remaining precipitated platinum is washed into a beaker, where it is heated with fairly
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strong HC1 until effervescence entirely ceases. This is t o remove any adhering A1 or other metallic impurities. Stirring a t this point will aid flocculation and make filtering easier. The P t is then washed onto the filter previously used and washed with hot water until free from acid. I t is then dried, ignited t o destroy the paper, and weighed. It is then dissolved in aqua regia and evaporated t o small volume several times t o remove C1 and H N 0 8 . This solution is filtered through a tared Gooch crucible and the weight of insoluble matter is deducted from the amount weighed as Pt. The weight of insoluble matter is usually a few centigrams and probably consists of unburned carbon from the filter paper. The platinum solution for use in analysis is of such strength t h a t I O cc. contain I g. of platinum. THEHORDALKALI PRODUCTS COMPANY LAKESIDE, NEBRASKA
SUGGESTIONS ON SOME COMMON PRECIPITATIONS By GEORGEH. BROTHER
Received October 20, 19 17
A number of my friends engaged in analytical work have spoken t o me about filtration difficulties they have encountered in some of the most common determinations. According t o their statements, they are unable t o get filters which will “hold” unless t h e y resort t o the very retentive, but comparatively slow papers. After considerable investigation of the subject, I have come t o the conclusion t h a t their blame is largely misplaced. The fault, in the great majority of cases, lies not so much in the paper used as in t h e method of precipitation. For this reason I a m giving a few “tricks of the trade” which, I a m sure, will be helpful t o any analyst not already acquainted with them, if used in standard methods given in any reputable reference, such as Treadwell-Hall. BARIUM SULFATE
The sulfate solution should be about 2 0 0 cc. in volume and weakly acid with hydrochloric acid (I cc, I . z sp. gr. t o a neutral solution). It should be heated t o a temperature just below boiling,l and about half of the solution of barium chloride necessary for excess added drop by drop, stirring well meanwhile, and allowed t o digest for about 5 minutes. The remainder of the precipitant is then added (not necessarily so slowly, though the solution should be stirred during the addition) and it is allowed t o digest I O or 15 minutes longer. I t is then ready for filtration. A precipitate formed in this way will be found quite crystalline and will be readily retained by a paper of moderately close texture. I have quite satisfactorily used Whatman 40, C. S. & S. 5 8 9 “White Ribbon,” and Munktell’s o instead of the slower Whatman 4 2 , C. S. & S. 5 8 9 “Blue Ribbon,” or Munktelrs 00. I n this way time may be saved in the filtration as well as in the much shorter period of digestion. 1 “Just below boiling” gives all the advantages of precipitation and digestion in hot solution and eliminates the risk of superheating and loss through frothing or bumping.
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y CALCIUM O X A L A T E
Heat t h e solution of the calcium salt t o just below boiling. Add excess ammonium oxalate solution, then just enough hydrochloric acid (sp. gr. 1.2) to dissolve the precipitate. Add ammonium hydroxide solution drop b y drop until distinctly ammoniacal, then run in a good excess. Digest a t a temperature just below boiling for about half an hour. Filter while hot and wash precipitate with hot water. The important point in this determination is the acid oxalate solution from which calcium oxalate is precipitated by t h e addition of ammonia. The formation of calcium hydroxide is in this way prevented and a crystalline precipitate of the oxalate insured. The method works out the same if the original calcium solution is made acid, the ammonium oxalate (or oxalic acid) added, then the ammonium hydroxide solution, as above. The objection t o this procedure is, of course, the absence of a n indicator t o prevent the addition of a n unnecessary excess of acid. For volumetric lime determinations, where an ashless paper is a n unnecessary extravagance, Whatman 3 and 3 0 or Munktell I O O will be found quite satisfactory if the precipitation is done by this method.
Vol.
IO,
No.
2
nesia mixture t o a n a m m o n i a c a l solution of t h e phosphate in the cold. The method of B. Schmitz, as outlined in Treadwell-Hall ( L o c . cit.), p. 434, gives much more satisfactory results. The phosphate solution is treated with excess magnesia mixture solution, hydrochloric acid added just t o dissolve the precipitate and i t is heated t o boiling. Ammonium hydroxide solution is added slowly until a crystalline precipitate forms. If the precipitate is not crystalline, it should be redissolved by the addition of hydrochloric acid and reprecipitated with ammonia. When a distinctly crystalline precipitate has formed, the solution is made ammoniacal, i t is removed from the hot plate and allowed t o cool. When cold, add a volume of ammonia (sp. gr. 0.9) equivalent t o about one-fifth the volume of t h e solution, and at the end of about 10 minutes it is ready t o filter. The reverse of these determinations, i. e . , t h e determination of magnesium by precipitating with a soluble phosphate, are carried out analogously. A number of chemists in brass work are having trouble with filtering tin dioxide. I have undertaken t o investigate this determination, and hope to have some results on it before long. OTTAWA,CANADA
AMMONIUM PHOSPHOMOLYBDATE
The principal difficulty with this precipitation is t h e adherence of many analysts to the old rule, v i z . , heat the phosphate solution t o about 70’ C., precipitate and digest a t no higher temperature. If this procedure is followed, digestion for several days is necessary t o secure a filterable precipitate, and even then success is uncertain. I have found t h e method of Woy with modifications, as given in TreadwellHall’s “Quantitative Analysis,” ( 1 9 1 5 ) ~p. 4 3 7 , t o be very satisfactory. The essential point of this method is precipitation and digestion a t a temperature ju‘st below boiling. The phosphate solution should be made distinctly alkaline with arinmonium hydroxide, then nitric acid added t o slight excess. This is a convenient way t o insure the presence of ammonium nitrate in the solution and prevents the addition of too great an excess of nitric acid. I t should be heated t o boiling, then, while stirring, add the ammonium molybdate solution drop by drop from a pipette. Digest on a hot plate at a temperature just below boiling until t h e supernatant liquid is clear and colorless (usually about 15 minutes). Decant, wash and filter as usual. Occasionally when the precipitant is added, no precipitate immediately forms, but instead t h e solution becomes colored yellow. Digestion, as described above, will bring about complete precipitation and conversion of the yellow solution t o colorless, but in such cases more than 1 5 minutes’ digestion is usually required. The precipitate thrown down in this way is coarse enough t o be retained by quite open-textured paperg such as Whatman I and 31, C. S. & S. 595, or Munktell’s OB. MAGNESIUM AMMONIUM P H O S P H A T E
Here, again, I think the difficulty lies in the use of old methods, which called for the addition of mag-
A NEW PORTABLE HYDROGEN SULFIDE GENERATOR By W. FAITOUTE MUNN Received November 5 , 1917
Because of t h e objections t o hydrogen sulfide generators in general, namely, the renewal of t h e acid, the leaking of gas following the completion of t h e precipitation after the supply is not further desired, and bulkiness, the following apparatus is recommended. The generator is quite light, practically in one piece, self-adjusting, made in a size adapted t o most analytical work, and is supported by a condenser clamp t o a n iron support, th
