228 Scientific Intelligence^ Sec 



When cyanogen is prepared from the bi-cyanidc of mercury, even 

 though perfectly pure, there is always a black matter left behind in 

 the retort. Mr. Johnston ascertained that the cyanogen given off* 

 was perfectly, pure, being all absorbed by caustic potash. Hence, 

 he inferred from the known composition of the bi-cyanide of mercury, 

 that this black matter must have the same composition as cyanogen, 

 and this both Leibig (whom he requested to submit it to analysis) 

 and himself have confirmed by experiment. The same substance is 

 also procured if the brown precipitate obtained, where the aqueous 

 or alcoholic solution of cyanogen is kept, be heated to redness in a 

 close vessel. Paracyanogen, as the author terms this compound, he 

 describes as a black or brownish-black shining substance not acted on 

 by any other menstruum but sulphuric acid. When thrown into 

 boiling nitric acid, a solution of paracyanic acid is obtained, giving 

 yellow or brownish salts, with persalts of mercury and salts of silver. 

 The composition of paracyanic acid, Mr. Johnston states to be (2 Az 

 4 C) O, thus differing entirely from cyanic, which is (Az 2 C) O. 



4. Mr. West submitted to the section a proposition for determin- 

 ing the quantity of various gases in the atmosphere by passing large 

 quantities of air through various absorbent liquids. Dr. Dalton, in 

 answer to this suggestion, stated that he considered the quantity of 

 carbonic acid in the atmosphere always as uniform, even in towns. 

 The quantity amounts to 1 in 1100. He stated that he had analyzed 

 air from the top of a high mountain, and had found the same quan- 

 tity of carbonic acid in it as in the air of the atmosphere. It was 

 generally understood in the section that Dr. Dalton had procured 

 the air by inverting a bottle of water ; the residual water of course 

 would absorb the carbonic acid, and it was in order to prevent this 

 source of error that Mr. West proposed to operate upon large quan- 

 tities. 



5. Dr. Hare read a printed paper (which was distributed among 

 the members of the chemical section at Edinburgh, two years ago) 

 on the nomenclature of Berzelius. 



• Thursday, 25th August. — 1. Dr. Daubeny stated that he had 

 found that the sublimation, (as he had considered it at the last meeting 

 of the association,) of carbonate of magnesia was entirely a mechanical 

 process. .Hence, the explanation of Von Buch of the formation of 

 Dolomitic rocks, viz., by limestone becoming impregnated with mag- 

 nesia through the agency of heat is incorrect. 



2. Dr. Dalton made som.e observations on Atomic Symbols, in 

 continuation of those made at the Dublin Meeting. 



3. Mr. Johyiston explained the use of some Chemical Tables, 

 which he exhibited to the section. 



4. Dr. Thomson read a paper on Mixtures of Sulphuric Acid and 

 Water ; in which he shewed that the theory of Iroine respecting 

 specific heat cannot be true. He offered a very simple explanation 

 of the cause of the evolution of heat when mixtures are made. 



The paper will appear in the next number of the Records. 



Friday, 26th August. — 1. 3Ir. Scanlan exhibited and described 

 a solid yellow body crystallizing in prisms, which rises when pyro- 

 lygneous acid is distilled over lime ; the latter saturating the acetic 



