LECTURE II.] HISTORY OF CHEMISTRY. 2Q 



standing over mercury. Besides the charcoal, the dish con- 

 tains a trace of phosphorus and tinder. By means of a bent, 

 red-hot, iron wire, he ignites the phosphorus, which communi- 

 cates the combustion to the tinder, and thus to the charcoal. 

 After the combustion of the latter has ceased, he takes out the 

 dish and weighs it, and so finds the quantity of the charcoal 

 burned. He measures the volume of gas in the bell-jar, absorbs 

 the carbonic anhydride by means of potash, and measures 

 again. In this way he obtains the volumes of the carbonic 

 anhydride produced and of the oxygen employed in the com- 

 bustion ; and hence, all the data necessary to calculate the 

 composition of carbonic anhydride. 



This he makes use of in carrying out the analysis of organic 

 substances, such as spirit of wine, oil, and wax. He had 

 satisfied himself, at an earlier date, that water and carbonic 

 anhydride are alone produced by the combustion of these 

 substances, whence he had quite correctly concluded that they 

 contain carbon, hydrogen, and oxygen only. In the estimation 

 of their quantitative composition, Lavoisier employs an appa- 

 ratus similar to that indicated above. For example, he places 

 a spirit lamp, which he weighs before and after, under the bell-jar, 

 and burns some of the spirit: he also determines the quantities of 

 carbonic anhydride produced and of oxygen employed, and from 

 these data he is able to calculate the composition of the spirit. 



With this I shall close the consideration of Lavoisier's 

 chemical investigations. A superficial estimate of his merits is 

 all that I have been able to give. It is only by a minute study 

 of his works that any complete idea of his significance, and 

 any proper understanding of how much our science owes to his 

 great intellect, can be obtained. There are, however, certain 

 directions of his activity that I have not even mentioned, as, 

 for example, the researches on respiration, about which I still 

 wish to say a few words. Priestley already knew that oxygen 

 was necessary for respiration. 43 Lavoisier shows how it is used 

 up in the lungs, in the formation of carbonic anhydride and of 



43 Compare p. 17, 



