60 SMITH'S INTERMEDIATE CHEMISTRY 



after the explosion, but is apt to break it by striking the top 

 violently. 



By taking the gases in the exact ratio 1 : 2, and surround- 

 ing the tube by a wider one through which steam passes, the 

 condensation of the resulting steam is prevented. It is found 

 that, when all the gases are measured at the same temperature 

 (here about 100), a shrinkage of one-third occurs. That is 

 to say: 



1 vol. Oxygen -j- 2 vols. Hydrogen 2 vols. Steam. 



Gay-Lussac's Law of Volumes. When other chemical 

 actions between gases are studied in the same way, it is found 

 that, in every case, the volumes of the gases used and produced 

 in a chemical change can always be represented by the ratio of 

 small whole numbers. This fact is exceedingly interesting. 

 It was first discovered by Gay-Lussac in 1808. There is no 

 such simple relation amongst the proportions by weight, which 

 usually can be expressed only by large numbers (see p. 36) or by 

 irregular fractions, so that this evidence of the existence of a 

 simple rule in regard to combining proportions is the first we 

 have encountered and is very welcome. The use made of it by 

 the chemist will be developed in the next chapter. 



Physical Properties. Water is without odor or taste. It is 

 very pale blue in color, as is shown when we look through a con- 

 siderable depth of water. 



Melting ice and freezing water have the same temperature. 

 The point at which the mercury column of a thermometer stands, 

 when the instrument is immersed in such a mixture of ice and 

 water, is marked on the centigrade scale. This is the freezing- 

 point of water. The density of ice is little over nine-tenths that of 

 water. 



When water is heated, it gives off vapor more and more freely 

 until finally it boils. This point is recognized by the fact that 



