300 British Association for the Advancement of Science. 



Dr. B. also communicated a |)aper " On the possibility oiohtaiii- 

 ing hy Voltaic action^ crystalline metals, intermediate between 

 the Poles or Electrodes," and exhibited a mass of plaster of Paris 

 (upon which he had operated) containing little veins of copper 

 disseminated through it in every direction, which presented a 

 marked resemblance to those met with on the large scale in na- 

 ture. 



Prof. Johnston described a compound of sulphate of lime, de- 

 posited from a high-pressure boiler, containing half an atom of 

 water, and in this particular differing from any other composition 

 of the kind. 



Mr. Phillips stated that the Blue Pigment submitted last year- 

 by Dr. Traill, was Prussian blue largely diluted, and rendered 

 pale by ferrocyanide of antimony. 



Prof Graham read a Note on the Constitution of Salts. He 

 wished to draw attention to a distinction in saline combinations 

 which is too often overlooked, and confusion thereby occasioned. 

 The orders of monobasic, bibasic, and tribasic salts, of which the 

 phosphates proved types, have lately been greatly enlarged by the 

 discoveries of Liebig and Dumas respecting vegetable acids, and 

 the distinctive characters of these orders are well understood. 

 The best proof that an acid is bibasic or tribasic is its combining 

 at once with two bases which are isomorphous, or belong to the 

 same natural family, — as phosphoric acid does with soda and 

 ammonia in microcosmic salt, and tartaric acid with potassa and 

 soda in Rochelle salt. Water and magnesia, water and barytes, 

 water and oxide of lead, are also constantly associated as bases 

 in bibasic and tribasic salts, but never in true double salts, or com- 

 binations of two or more salts with each other, with which salts 

 of the preceding orders are often confounded. But it is too gen- 

 erally supposed that a metallic oxide cannot exist in a saline com- 

 bination, except in the capacity of base, although in most of those 

 bodies which are at present termed sub-salts, the whole or a por- 

 tion of the rnetallic oxide is certainly not basic, but is attached to 

 a really neutral salt, in a capacity similar to that of constitutional 

 water, or water of crystallization. The test of the non-basic 

 character of water or a metallic oxide in a compound, is the ab- 

 sence of a parallel combination containing an oxide of the potash 

 class. , 



