Chemical Science. 379 



correct, except for cases where gas at 32° is to be estimated at some 

 other temperature. Mr. Biggs has pointed out this error in the 

 Annals of Philosophy, vi. 415, and has given the following more cor- 

 rect rule. Add the degrees which the gas is above 32° to 480, add 

 also the degrees which the required temperature is above 32° to 4S0, 

 then as the first number is to the second, so is the volume of the gas 

 to the volume required. Another rule for making the correction is, 

 to add the number of degrees between 32° and the temperature of 

 the gas to 480, divide the volume of the gas by the sum, and multi- 

 ply the quotient (which will be the expansion for each degree) by 

 the number of degrees between the temperature of the gas, and the 

 required temperature ; if the latter be greater than the former, add 

 the product to the volume of gas, if it be less subtract it, and the 

 corrected volume will be given. 



10. Supports for Ignition of Particles by the Blow-pipe.— The 

 sappare is a substance recommended by M. de Saussure, for the sup- 

 port of minute particles intended to be subjected to the action of the 

 blow-pipe, but is seldom used in consequence of the difficulty of 

 making the particle adhere to it. In place of the water, saliva, or 

 gum-water, generally used, Mr. Smithson recommends the use of a 

 mixture of water and refractory clay ; a little of the moist clay is to 

 be taken up on the end of the splinter of sappare, and the particle to 

 be heated being touched by it adheres, the whole is laid aside for a 

 few minutes, and is then dry and may be heated. Mr. Smithson also 

 recommends small triangles, or slender slips of baked clay in lieu of 

 sappare, which is not always to be had. Another more recent pro- 

 cess is, to file the very end of a platina wire flat, place the minutest 

 portion of the moist clay on it, and then touch the particle to be 

 heated. In a few moments it is dry, and may be put into the flame 

 without flying off, unless too much clay has been taken. 



Mr. Smithson points out a remarkable difference between quartz 

 and flint before the b'ow-pipe. Quartz is almost refractory, but flint 

 fuses with facility, swells, and even froths. It is aked whether flint 

 does not, like pitch-stone, contain bitumen, which at a certain heat 

 tends to tumefy it? — Ann. Phil. N. S. vi. 412. 



1 1. Solubility of Substances induced by Tartaric Acid. — The fol- 

 lowing observations on solubility conferred by tartaric acid, are given 

 in a note by M. Rose, in a .Memoir on Titanium. " It is known that 

 a solution of peroxide of iron containing tartaric acid, cannot be 

 precipitated by caustic alkalies, by their carbonates, or succinates ; its 

 presence is indicated only by tincture of galls, ferro-prussiate of iron 

 and hydro-sulphurets. I thought, therefore, 1 should obtain an oxide 

 of titanium perfectly pure, by mixing tartaric acid with a solution 

 containing the oxides of iron and titanium, and then adding ammonia 

 to precipitate the oxide of titanium. But I found that many solutions 



