WATER. 



Dr. Thomson (First Principles,) employed 42 volumes of hy- 

 drogen to 100 of air, and always obtained a reduction of 60, one 

 third of which, 20, corresponds with the theory of volumes, and also 

 of multiple proportions by weight, and granting that atmospherical 

 air is a feeble compound, this would appear to be, in all probability, 

 the true proportion ; and if this is the true proportion, this fact in its 

 turn strengthens very much the opinion that in the atmosphere, the 

 elements are not merely mixed, but slightly combined. 



The electric spark will no longer cause explosion in the mixture 

 of 2 volumes of common air, and 1 of hydrogen gas, when there are 

 12 parts of common air, or 9 of hydrogen added to the mixture, or 

 when it is rarefied 16 times by diminution of pressure, or 6 times by 

 heat. Oxygen and hydrogen gases in the proportion to form water, 

 if rarefied mechanically 1 8 times, will not explode by electricity ; 

 according to Sir H. Davy, rarefaction by heat causes the mixed 

 gases to explode more readily by the temperature of ignition. 



In the analysis of atmospheric air by hydrogen gas, 5 volumes 

 of air should be , sufficient for 2 of hydrogen; but it is better to 

 employ a small excess ; here, as before, one third of the dimi- 

 nution will be owing to oxygen. Dr. Hare says, that in a great 

 number of experiments, performed by means of his instruments, he 

 obtained very constantly 20.66 as the quantity of oxygen in 100 

 parts of the air, and that in twenty experiments, the greatest discord- 

 ance did not amount to T oVo- m 100 measures of air. Comp. 



ACTION OF PLATINUM. 



(a.) A very effectual eudiometer was unexpectedly presented to 

 us by a discovery of Dobereiner, of Jena. The muriate of platinum 

 and ammonia, when ignited, leaves the metal in the state of spongy 

 platinum,* upon which, if a stream of hydrogen be directed, the metal, 

 if air has access, becomes ignited, and the gas soon takes fire. 



(6.) It is necessary that the oxygen gas of the air be let in at the 

 same time, and water is the result, as if the gases had been kindled 

 in any other way. 



(c.) If spongy platinum be introduced into a mixture of oxygen, or 

 common air, with hydrogen gas, in explosive proportions, they de- 

 tonate ; in other proportions they slowly combine and form water. 



(d.) The spongy platinum being formed into a paste, with about an 

 equal weight of alumine, or china clay, and water, with the addition 

 of some muriate of ammonia, to preserve the porosity, and made into 



* Or the sub-oxide of platinum, prepared by Mr. E. Davy's process, answers, per- 

 haps equally well. 



t See Henry, Vol. I. p. 238, and Ann. de Chimie et de Phys. 23, and 24. 



