CHEMISTRY OF THE SEVENTEENTH CENT. 231 



spring, as he calls it, of air, and his name is properly associated with 

 that well-known law which he was the first to announce. This law, 

 which was some years afterwards again discovered independently by 

 the French physicist Mariotte, and is often called by his name also, 

 is that the space occupied by a given mass of air varies inversely as 

 the pressure. 



Boyle expressed great doubt about the truth of either the ancient 

 or the alchemical theory of elements. Thus he defies any one to show 

 him the decomposition of gold into sulphur, mercury, and salt, and 

 clearly points out the absurdity of the method of attempting to de- 

 compose bodies by heat, the result being in reality the formation of 

 new compounds. Boyle was the first to draw a distinction of funda- 

 mental importance in chemistry between compounds and mixtures. In 

 the former the constituents entirely lose their original properties, and 

 these constituents cannot be mechanically separated from each other, 

 whereas in mixtures the characteristic properties of each ingredient is 

 perceptible, and they can easily be separated from each other by other 

 than chemical means. 



Boyle was the first to devise a method of collecting gases. He in- 

 verted a vessel filled with water containing sulphuric acid in another, 

 and placed underneath the mouth of the inverted vessel some iron 

 nails. This gas, as we know, was hydrogen ; but Boyle did not ex- 

 amine so much its chemical as its physical properties. The experiment 

 was regarded by him as a new instance of the production of air by an 

 artificial method. Boyle made a vast number of experiments on the 

 evaporations of various liquids, in the air and in a vacuum ; on ebulli- 

 tion ; on the congelation of water ; on the barometer, etc. He made 

 observations on the effects of placing animals of every kind in the 

 vacuum of the air-pump. He proved in this way that fish require to 

 breathe air dissolved in the water. 



The origin of the rust which appears on metals was a question often 

 discussed by the chemists of the seventeenth century. Boyle remarks 

 that verdigris and the rust of iron are produced by corrosive effluvia 

 in the air, and that it is by the study of these products that the com- 

 position of the air will be ascertained. After describing a great number 

 of experiments, he comes to the conclusion that there is in the air some 

 vital substance which plays a part in such phenomena as combustion, 

 respiration, and fermentation. When this substance has once been 

 consumed, flame is instantly extinguished, and yet the air thus extin- 

 guishing flame has had very little of its substance removed. In a trea- 

 tise entitled " Fire and Flame weighed in a Balance," Boyle describes 

 a series of experiments on the increase of the weight of metals (lead, 

 copper, tin) by calcination. As he obtained results not differing much 

 whether the crucible in which the metal was heated was opened or 

 covered, he did not trace the effect to the air, but attributed it to the 

 fixation of the particles of fire which passed through the pores of the 

 crucible. 



