RECENT ADVANCES IN SCIENCE 293 



at four, whilst its greatest positive valency (chlorine, oxygen) 

 determined with any certainty is never greater than three. 



Further advances in the domain of preparative work 

 come from Franklin (/. Amer. Chem. Soc. 37, 852, 191 5). In 

 this fruitful field of reaction (liquid ammonia) a potassium 

 ammonoargenate, AgNHK NH 3 , has been produced by the 

 combination of silver amide with potassamide. A crystalline 

 compound separates out, in which the terminal NH 3 mole- 

 cule may be looked upon as " ammonia of crystallisation," 

 analogously to " water of crystallisation." 



By a study of equilibrium relationships of aqueous potas- 

 sium and sodium sulphates at various temperatures Okada 

 {Mem. Coll. Sci. Kyoto, 1, 95, 1914) draws the conclusion that 

 a double salt K 3 Na(S0 4 ) 2 has a stable existence. If correct 

 such a salt would clearly indicate the superior electro-positivity 

 of the potassium atom when matched against the sodium atom. 



Another sulphate, that of cadmium, which is found in the 

 solid state to have empirically the abnormal formula CdS0 4 

 8/3H 2 0, has been the subject of investigation by Blomberg 

 (Zeitsch. anorg. Chem. 91, 248, 191 5). In concentrated solu- 

 tions, according to Noyes and Drucker, ionisation would take 

 place according to the following equation : 



3 CdS0 4 $ [Cd 2 S0 4 ] - + [Cd(S0 4 ) 2 ]." 



If now, Blomberg points out, the two complex ions com- 

 bine together when crystallisation takes place, it is possible 

 for a hydrate to be formed which will not contain a number of 

 water molecules exactly divisible by three. 



Analytical. — Perhaps the most important progress we 

 have to report under this heading is the compilation and 

 publication by the Institute of Chemistry of a " List of Reagents 

 for Analytical Purposes." This important publication gives 

 a list of the finer chemicals obtainable from British manu- 

 factures along with the standards of purity to which each rea- 

 gent attains and the tests, namely, those adopted by the 

 Eighth International Congress of Applied Chemistry, which 

 have been applied. Some such work as this has been badly 

 needed, not only by analytical chemists, but by all workers 

 in the wider field of chemistry, and it is sincerely to be hoped 

 that the Institute of Chemistry will continue their good work 

 by enlarging and revising the List from time to time. 



