348 • Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE 



I. Chemistry and Physics. 



1. A Rapid Process for the Determination of Phosphoric Acid. 

 — H. CoPEAU lias described a new method for this determination 

 which deserves notice on account of its unusual features, and 

 because it is very simple and rapid in its execution. It is based 

 upon the fact that when phosphoric acid in the presence of another 

 acid, such as sulphuric, is shaken with ether and an alkaline 

 molybdate phosphomolybdic acid is formed which combines with 

 ether and water to form a dense yellow liquid which is immisci- 

 ble with the mother liquor. When equilibrium is established 

 there are three liquid phases, an excess of ether, an aqueous solu- 

 tion and the yellow phosphomolybdic acid liquid. A reaction of 

 this kind w^as first observed by Marignac in connection with 

 silicotungstic acid, w^hile the phosphomolybdic reaction was 

 employed by Drechsel in 1887 in connection with the prepara- 

 tion of complex acids, but not for analytical purposes. 



The j^ellow liquid was found to be practically constant in com- 

 position and to contain 1.73 percent of P2O5, with about 44 per- 

 cent of phosphomolybdic acid, the 1 :24 compound, 33 percent 

 of ether and 22 of water, and its specific gravity was found to be 

 1.23. With as little as 1 mg. of phosphoric acid a distinct globule 

 of the yellow liquid was obtained amounting to about ^ cc. 

 Reference to the original article must be made for the full details 

 in regard to the reagents and the method, but it may be stated 

 that the process is carried out in special flasks of about 60 cc. 

 capacit}^ which are provided with slender, graduated* prolonga- 

 tions at the bottom for measuring the yellow liquid, and that the 

 latter is collected by whirling the flasks in a centrifuge. 



It was found that after the solution of phosphate was ready the 

 time required for a determination was only about 15 minutes. A 

 few test analyses were made showing excellent results. The only 

 interfering substance mentioned is citric acid. — Comptes Rendus, 

 175, 656 (1921). h. l. w. 



2. The Existence of Tetrahydrated Sodium Sulphate in Mix- 

 Crystals with Sodium Chromate. — Theodore W. Eichards and 

 W. BuELL Meldrum have shown that in addition to the well- 

 known isomorphic crystalization of Na2SO4.10H2O and Na2Cr04. 

 IOH2O in all or almost all proportions, the tetrahydrate of 

 sodium chromate is also capable of isomorphously dissolving 

 sodium sulphate, in spite of the fact that Na2S04.4H20 does not 

 exist by itself. 



This induced crystallization of one salt by another in an other- 

 wise non-existing form is well known in several other cases ; as, 

 for instance, CaS04.7H20, otherwise unknown, with FeS04.7Il20. 



