3/2 NINETEENTH CENTURY. pt. hi. 



Cumberland. He received the ordinary education of a village 

 school, and after being master of a small academy at Kendal, 

 he went to Manchester, where he supported himself all the 

 rest of his life by teaching mathematics. 



Fortunately for science, a blind gentleman named Gough 

 became interested in him, and gave him the use of his 

 library and chemical laboratory, which enabled Dalton to 

 work out many useful facts, and to establish the laws which 

 are now the guide of all chemists, though they differ about 

 some of his conclusions. 



You will remember that it was only in the time of 

 Lavoisier that chemists began to weigh carefully the gases 

 into which substances can be decomposed. Before then it 

 had been thought sufficient to say that a substance contained 

 sulphur, mercury, carbon, &c., without saying how much of 

 it there was. But after the discovery of oxygen, when the 

 real nature of chemical change began to be understood, 

 chemists saw the importance of weighing accurately the 

 different elements into which a substance can be broken up ; 

 and when this had been done for some time, and a great 

 number of analyses had been made, it was seen that any 

 given chemical compound always contains the same elements 

 combined in the same proportion. 



Thus, for example, all water, whether it comes from rain, 

 snow, dew, steam, or exploded oxygen and hydrogen, will 

 always be found to contain two parts by weight of hydrogen 

 to sixteen parts by weight of oxygen ; so that if you decom- 

 pose 1 8 ounces of water you will collect 



2 volumes of hydrogen weighing I oz. each . . 2 ozs. 

 I volume of oxygen weighing 1 6 ozs. . . . i6 ozs. 



1 8 ozs. 



