442 Analyses of Books, [Djec. 



lime, be composed of one atom lime and one atom acid, then an 

 atom of fluoric acid will weigh 1-299. It appears from this result 

 that the atom of fluoric acid is the lightest of all the acids, and that 

 it cannot contain more than a single atom of oxygen. This is cer- 

 tainly against the common opinion respecting the composition of 

 fluoric acid ; as we are not acquainted with any other acid that 

 contains so little oxygen as a single atom. 



But according to Sir H. Davy's view of the matter, Derbyshire 

 spar is a compound of fluorine and calcium. Now 73*58 lime 

 contain 20*32 oxygen ; so that according to this view the spar i* 

 composed of 



Fluorine 4674 100 



Calcium 53'26 113-95 



100-00 



If we suppose this a compound of an atom of calcium and an 

 atom of fluorine, an atom of fluorine will weigh 2'299. 



Davy has given some other analyses of the fluates, which it may 

 be worth while to state : 22 grains ot fused subcarbonate of potash 

 (containing 31 per cent, of carbonic acid,) formed 18-15 grains of 

 dry fluate of potash. These 18-15 grains, treated with sulphuric 

 acid, gave 38*5 of bisulphate of potash. 100 parts of solution of 

 ammonia, of the specific gravity 0-9162, require for saturation the 

 quantity of fluoric acid contained in 32 grains of fluate of potash. 



The second part of this paper contains an account of a number 

 of unsuccessful attempts to obtain the base of silica in a separate 

 state. When silica is heated with potassium it is decomposed ; but 

 the base cannot be separated from the alkali by means of water, as 

 it decomposes that liquid, and is converted again into silica. But 

 Sir H. Davy has rendered it very probable that the base of this 

 earth is not a metal, but a substance analogous to boron in its 

 properties. 



The last part of this paper consists of a statement of the reasons 

 why chlorine should be considered as an undecompounded sub- 

 stance, and muriatic acid as a compound of chlorine and hydrogen. 

 This part of the paper is remarkably well drawn up, and is written 

 in a style of clearness and elegant simplicity, so much to be desired 

 in philosophical writings. 



6. Some Experiments and Observations on a New Substance, 

 which becomes a Violet-coloured Gas by Heat. By Sir Humphry 

 Davy, Knt. LL.D. F.R.S. — This substance, now familiar I pre- 

 sume to most British chemists, was discovered about three years ago 

 by M. Courtois, a saltpetre-maker in Paris. It was first examined 

 by Clement and Desormes, and afterwards by Gay-Lussac. The 

 present paper contains Sir H. Davy's experiments on it. 



This substance, called iodine from the violet -coloured vapour 

 which it forms when heated, is obtained from kelp, or spent 

 soapers' leys j and French kelp vields a much greater proportion of 



C 



