22 PRACTICAL AGRICULTURAL CHEMISTRY [-56-57 



tube of gas burns quietly. To prevent accidents it is better 

 to cover the Woulffe's bottle with a glass-cloth. 



When the hydrogen is free from air ignite the stream of 

 gas and hold over the flame a clean, dry beaker. After a 

 time drops of water will collect inside the beaker, which 

 will be found to have the ordinary properties of pure water. 



EXPERIMENTS ON WATER 



56. Natural Waters. — Dissolved substances are 

 always present in the water which occurs in nature. Even 

 carefully collected rain-water contains some impurities dis- 

 solved out of the air. Spring, river, and well waters con- 

 tain also dissolved matters, obtained from the soil or rock 

 with which they have been in contact. 



57. Distillation of Water.— The water obtained 

 from the general supply of a town is seldom sufficiently 



Fig. 22 



pure for use in a laboratory, as it contains several substances 

 in solution. It may be freed from these impurities by the 

 process known as distillation. The apparatus required for 

 this operation is shown in fig. 22, and consists of a retort 

 whose neck leads into a flask which is kept as cool as 

 possible by being immersed in a vessel of water. Half fill 

 the retort with water and heat it with a Bunsen flame, prefer- 



