CHEMICAL APPARATUS AND PRODUCTS. 205 



It must not, however, be supposed that we even now possess a 

 complete system ; the equation 



shows that 4 vols. of hydrogen combining with 2 vols. of oxygen 

 produce 4 vols. of steam, and also that 4 parts by weight of 

 hydrogen uniting with 32 parts by weight of oxygen form 36 of 

 water ; but there is one thing that it does not show, that is, the 

 development of an immense quantity of energy in the form of 

 heat. This the phlogistic theory did indicate, but nothing else. 

 So, as has been pointed' out by Professor Crum Brown, the true 

 representation of chemical action is probably contained in a com- 

 bination of the atomic theory and the theory of phlogiston, if 

 for the term phlogiston we substitute potential energy. 



On consulting the works of the earlier chemists it is impos- 

 sible to avoid being struck by the almost universal employment 

 of fire in their operations ; furnaces being described and depicted 

 for large numbers of processes, many of which were carried on 

 for days, for months, or even for years. This is, no doubt, due 

 to the devotion to the study of the metals in the search for the 

 philosopher's stone. The recent progress of organic chemistry 

 and the use of gas for fuel has perhaps been the cause of some 

 neglect of furnace operations, but the invention of gas furnaces 

 giving very constant temperatures will probably direct the atten- 

 tion of chemists once more to the application of elevated tem- 

 peratures, and a simple instrument for measuring the temperature 

 will materially aid in bringing the processes to perfection. 



SPECIFIC GRAVITIES OF GASES AND VAPOURS. 



The close relation existing between the molecular weight of a 

 gas and its specific gravity, renders the determination of the den- 

 sities of gases and of the vapours of volatile liquids and solids a 

 matter of great importance to the chemist, as he is often able, by 



