Chemical Science. 427 



8. The force of expansion spoken of is essentially distinct from 

 that by wliich bodies tend to form vapour: for the degree of this 

 force has no relation to the degree of evaporability, and some- 

 times has a contrary ratio. 



9. This force has, in common with the forces of electricity and 

 magnetism, the power of increasing its proper action in the direc- 

 tion of the angles, of rendering it more intense, and of determin- 

 ing a current of matter in that direction. 



10. Finally, The effects of this force are not limited to mere 

 expansion, but consists also in chemical changes, decomposition 

 taking place, and re-compositions being produced. 



2. Effect of Heat on the colour of the Ruby. — in subjecting ru- 

 bies to high degrees of heat. Dr. Brewster observed a very singu- 

 lar effect produced during their cooling. At a high temperature the 

 red ruby becomes green ; as the cooling advances, this green tint 

 gradually fades and becomes brown, and the redness of this brown 

 tint gradually increases till the mineral has recovered its primitive 

 brilliant red colour. A green ruby suffei'ed no change from heat, 

 and a bluish green sapphire became much paler at a high heat, 

 but resumed its original colour by cooling. Edin. Journ. vi. 379- 



3. Pyrometer. — Mr. Sivright, proposes to remove the objections 

 to Mr. Wedgewood's pyrometer, in consequence of the irregular 

 contraction of the clay-pieces used, by substituting for them pieces 

 of agalmatolite, or figure-stone of China. In making experi- 

 ments on this substance, he has found it capable of contracting 

 in its dimensions considcrabl}', by heat, without any other change, 

 and he considers that its use will be advantageous, 



4. Source of Cadmium. — Mr. W. Herapath states, that he has 

 obtained cadmium in abundance from the zinc works near Bristol. 

 Zinc is obtained by putting calamine with small coal into a cru- 

 cible, which being closed at top, has a tube proceeding through 

 its bottom, into a vault below ; beneath the tube is a vessel of 

 water, and a short tube is at hand to connect at a proper time 

 with the long one, so as almost to reach the water. The work- 

 men do not connect until the " broxcn blaze" is over, and the 

 " blue blaze^' begun. This brown flame is owing to cadmium, the 

 oxide of which attaches itself to the roof of the vault, in greatest 

 quantity just over the orifice. It is mixed with soot, sulphuret 

 of cadmium, and oxide of zinc. Some portions contain from 

 twelve to twenty per cent, of cadmium. 



The metal is obtained by dissolving this substance in muriatic 

 acid, filtering, evaporating to dryness, re-dissolving and filtering, 

 and preci|)itating by a plate of zinc. The cadmium thrown down 

 is to be mixed with a little lamp-black or wax, put into a black 



