708 MODIFICATIONS OF ORGANIC COMPOUNDS. 



shewn by Dr. Clark that when certain corrections are made on 

 the calculations of Berzelius' experiments, they really give a 

 number for carbon nearly approaching to this. 



To give the process of organic analysis all the precision of 

 which it is susceptible, M. Dumas requires attention to the 

 following circumstances. 1 . To triple at least the quantity of 

 matter usually employed. 2. After the ignition of the com- 

 bustion tube to pass through it a large quantity of oxygen, so 

 as to burn the deposited carbon and re-oxidate all the copper, 

 which gets rid of the carburet of copper. 3. For the reception 

 of the water to employ a chloride of calcium tube accompanied 

 by a tube filled with fragments of pumice impregnated with oil 

 of vitriol. 4. To absorb the carbonic acid, Liebig's bulb ap- 

 paratus containing solution of potash is to be used, accompanied 

 by tubes containing potash moistened with the potash ley on 

 one side, and dry potash on the other ; the dry potash arrests 

 the water with which the gas has become charged by passing 

 through the liquid in the bulbs.* The most important obser- 

 vation of Dumas is that the combustion of the carbon is never 

 complete, unless oxygen be passed through the tube containing 

 the mixture of oxide of copper and matter to be analysed, and 

 the matter be thus burned in an atmosphere of oxygen. This 

 is the principle of the method of organic analysis originally prac- 

 tised by Dr. Prout, by which he was led to the conclusion that 

 the atom of carbon is exactly 6 on the hydrogen scale, or 75 

 on the oxygen scale.J M. Dumas, who now adopts this con- 

 clusion, has therefore been conducted to it by a recurrence to 

 Dr. Prout's own mode of investigation. 



MODIFICATIONS OF ORGANIC COMPOUNDS PRODUCED BY 

 ARTIFICIAL PROCESSES. 



IT is generally stated that no substances properly organic can 

 be produced by directly uniting their ultimate elements ; 

 although a few organic compounds may be formed from subs- 



* Annales de Chimie et de Physique, 3me Se"rie, tome 1, p. 39, where the im- 

 proved process is minutely described and the apparatus figured, 

 t Phil. Trans. 1827; or Brande's Manual of Chemistry, p. 1060. 



