TRANSACTIONS OF THE SECTIONS. 59 



On a new Compound of Sulphate of Lime with Water. 

 By Prof. Johnston, F.R.S. 



This compound is represented by 2Ca S + H, and occurs in masses 

 of a minute radiated structure, in minute cj'lindrical crystals, and in 

 large six-sided prisms. It is formed as a sediment in the boiler of a 

 steam engine at the Team Colliery, near Newcastle. The boiler is 

 worked under an average pressure of about two atmospheres. {See the 

 Loud, and Ed. Phil. Mag. for Nov. 1838.) 



On a new Compound of Bicyanide with Binoxide of Mercury. 

 By Prof. Johnston, .F.Ii.S. 



When dilute hydrocyanic acid is digested on red oxide of mercury 

 in excess, a white nearly insoluble compound is formed, which may be 

 separated from any soluble bicyanide which may be present in the su- 

 pernatant liquid by collecting it on the filter. Boiling water dissolves 

 the new compound, and leaves the excess of oxide of mercury. On 

 cooling, the salt is, in a great measuie, deposited on the sides and bot- 

 tom of the vessel in minute, pure, white, transparent, prismatic needles. 

 This salt is anhydrous, its solution has an alkaline reaction, and it con- 

 sists of equal atoms of the two mercurial compounds, or it is (HyCyc, 

 + HyOj). When heated in a tube, it decomposes with a slight deto- 

 nation, giving off carbonic acid, nitrogen, cyanogen, and metallic mer- 

 cury, leaving a black residue (para-cyanoge?t). Neutralized by nitric 

 acid, it gives a beautiful salt in long, delicate, quadrangular prisms, 

 which are represented by HyCyo + (HyO^ + | NO^), and are very 

 soluble in water. It gives also with acetic acid, a crystalline compound, 

 in which the quantity of acid appears to exist in a still smaller propor- 

 tion. With acid nitrate of silver, it gives Wohler's salt (HgCyg + 



AgN + 4H), nitrate of mercury remaining in solution. With neutral 

 nitrate of silver and various other salts, it gives crystalline compounds. 



On some supposed Exceptions to the Law of Isomorphism. 

 By Prof Johnston, F.R.S. 



In this paper the author endeavoured to show, that if the chemical 

 analyses and crystalline measurements of certain groups of substances 

 are to be depended on, the law indicated by previous researches, that like 

 forms indicate like formulce, is not universally true. The paper does 

 not admit of abridgement, but may be consulted in the Loiid. and Ed. 

 Phil. Mag. for Dec, 1 838. See also Reports of the British Association, 

 Vol. VL,p. 173, etseg. 



