Society of Arts, A&tpkt. — Wernerian Society. 409 



without the necessity or risk of calculations, which almost 

 always involve errors. 



A part of a letter from Dr. Henry to Mr. Davy, on ox- 

 ygen of ammonia when exposed to electrization, was read. 

 By some recent experiments Dr. H. has ascertained, that m 

 decomposing the ammonia, some oxygen was admitted in 

 the process, and that consequently^what wa3 found as the 

 result of Ins former experiments was not derived from the 

 ammonia by electrization, but from the agents employed. 

 The final result, however, of his experiments proved that 

 ammonia, as Mr. Davy originally concluded, is composed 

 ofoxvgen, hydrogen, and nitrogen. 



The Society then adjourned over one Thursday on account 

 of the holidays. 



SOCIETY OF ARTS, ADEtPHl. 



At a late meeting of this Society, a communication from 

 Mr. R. Porrett jun. wp.s read, announcing that he suc- 

 ceeded in obtaining prussous (or sub-prussie) acid — an ac.i 

 differing from prussic, as sulphurous does from sulphuric acid, 

 by containing less oxygen. It is a most delicate test of the 

 presence of silver in solution, and has the singular property 

 of precipitating iron of a red colour. It has completely- 

 proved the presence of oxygen in prussic acid ; as by de- 

 oxv^enating the latter it becomes prussous acid ; and oa 

 adding oxygen, it is again capable of affording a blue preci- 

 pitate of iron. 



A new process for hardening the surface of casts in plan- 

 ter of Pari^ has been communicated to the same Society. 

 It consists in boiling the cast in a solution of one pound of 

 alum in a pint of water for 15 minutes, and then suffering 

 it to dry gradually for about a month ; in this way the cast 

 acquires a very considerable degree of hardness upon its sur- 

 face, and is even capable of receiving a polish by friction, 

 so as to resemble white marble ; and the surface of it may 

 be cleaned from lime to lime, without the Jea^t injury to 

 the sharpness of the cast. 



WERNERIAN NATURAL HISTORY SOCIETY. 



At the meeting of this Society on the 8th ol April, there 

 was read the first part oi' a Description oi the Mineral Strati 



of 



