APPENDIX. 661 



of calcium tube being weighed gave the quantity of water evolv- 

 ed. The carbonic acid in the jar, over mercury, was absorbed 

 by a small glass of potash exactly weighed. The increase of 

 weight gave the quantity of carbonic acid evolved. The glass 

 tube containing the matter to be analyzed was strengthened by 

 a ribbon of tin plate wrapped round it, and it was heated to red- 

 ness, beginning at the end next the receiver, and passing back- 

 wards to the lower extremities. 



The determining of the water and carbonic acid by weighing 

 was a considerable improvement upon the process of Gay-Lussac 

 and Thenard, But the apparatus was rather too complex, and 

 the number of joinings too many. It would be difficult in this 

 country, where our corks are bad, to make it always air-tight. 

 Berzelius subjected from nine to ten grains of the substance un- 

 der experiment to analysis. He analyzed thirteen vegetable 

 substances, and as usual his results approached pretty near the 

 truth. 



About the year 1813, Gay-Lussac suggested to" M. Chevreul 

 the substitution of black oxide of copper for chlorate of potash 

 in the analysis of vegetable and animal substances. * M. Gay- 

 Lussac had employed this substitute in his analysis of the com- 

 pounds of cyanogen, f In 1816, the use of it was highly com- 

 mended by Dobereiner,J who does not seem to have been aware 

 of its previous employment in organic analyses in France ; at 

 least he takes no notice of it. 



In 1827, Dr Prout published in the Philosophical Transactions 

 a memoir entitled On the Ultimate Composition of Simple Alimen- 

 tary Substances.^ He had been occupied with these analyses for 

 many years, had tried all the different methods of analysis re- 

 commended by preceding experimenters, and had found them all 

 attended with difficulties that prevented him from attaining the 

 requisite degree of accuracy. This induced him to have recourse 

 to the combustion of the substances to be analyzed in a tube filled 

 with oxygen gas. The matter to be analyzed was mixed with the 

 requisite quantity of oxide of copper. It was then introduced into 

 the tube. The apparatus was filled with the requisite volume of 

 oxygen gas, the heat of a lamp was applied to the tube contain - 



* Ann. de Chim. xcvi. 53. f Ibid. xcv. 154, 184, 187. 



| Schweigger's Jour. xvii. 369. Phil. Trans. 1827, p. 385. 



