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) t o 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 a n d wash precipitate with hot water. The important point in this determination is t h e 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 t h e oxalate insured. The method works out t h e same if t h e original calcium solution is made acid, the ammonium oxalate (or oxalic acid) added, then t h e ammonium hydroxide solution, as above. The objection t o this procedure is, of course, the absence of a n indicator t o prevent t h e 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.
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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 t h e precipitate and i t is heated t o boiling. Ammonium hydroxide solution is added slowly until a crystalline precipitate forms. If t h e precipitate is not crystalline, it should be redissolved b y t h e 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 t h e hot plate and allowed t o cool. When cold, add a volume of ammonia (sp. gr. 0.9) equivalent t o about one-fifth t h e volume of t h e solution, and at t h e 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 t o 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 t o t h e 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 t h e 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 b y drop from a pipette. Digest on a hot plate at a temperature just below boiling until t h e supernatant liquid is clear a n d 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 t h e yellow solution t o colorless, b u t in such cases more t h a n 1 5 minutes’ digestion is usually required. The precipitate thrown down in this way is coarse enough t o be retained b y 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 t h e difficulty lies in t h e use of old methods, which called for t h e 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, t h e renewal of t h e acid, the leaking of gas following t h e completion of t h e precipitation after t h e supply is not further desired, and bulkiness, t h e 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
