16 Prof. H. Rose on the Inorganic Constituents 



form a principal constituent, the carbonized mass frequently 

 requires to be washed for several weeks. 



It sometimes happens that the aqueous solution appears of 

 a brownish colour, which depends upon the imperfectcarboniza- 

 tion of the substance. Usually the liquid becomes decolor- 

 ized on concentration, and deposits woolly flakes of carbon, 

 which may be easily separated by filtration, before other sub- 

 stances are deposited from it. 



If alkaline carbonates exist in the aqueous solution in any 

 considerable quantity, free alkali is formed by the action of the 

 carbon upon the alkaline carbonate, with the evolution of car- 

 bonic oxide. If the aqueous solution be evaporated, the dry 

 mass contains more or less hydrated alkali with alkaline car- 

 bonate. By means of a solution of nitrate of silver, we may 

 readily convince ourselves of the decomposition of the car- 

 bonic acid in the alkaline carbonates by carbon, since, unless 

 the mixture has been exposed to a very great heat, this re- 

 agent does not produce a pure white precipitate in the filtered 

 aqueous solution, but a more or less brownish precipitate is 

 formed, which contains oxide of silver as well as the white 

 carbonate of silver. 



Decomposition of the alkaline carbonates ensues principally 

 when the organic substance during its carbonization evolves 

 a very large quantity of olefiant gas. Hence it takes place to 

 a great extent when such seeds as contain a large amount of a 

 fatty oil are carbonized, as rape-seed ; it occurs to a much less 

 extent on the carbonization of other seeds which do not con- 

 tain any remarkable quantity of fatty oil, as peas, and likewise 

 with the herbaceous parts of plants. 



Unfortunately my attention was not directed to this circum- 

 stance until all the experiments described in the Appendix 

 were entirely or partly finished. The alkali among the con- 

 stituents of the aqueous extract is therefore assumed as exist- 

 ing in the state of hydrate. 



It is therefore advisable to pass a current of carbonic acid 

 gas through the aqueous solution before evaporating it, so as 

 to convert the hydrated alkali into the state of alkaline car- 

 bonate. 



The aqueous solution is then evaporated to dryness in a 

 platinum capsule. It usually happens that when the liquid 

 is very concentrated, it becomes more or less turbid from 

 the separation of phosphate of lime which was in solution. 

 When the liquid has been evaporated to a small volume, 

 the phosphate of lime which has separated may be removed by 

 filtration ; it is however difficult to free the aqueous solution 

 from it perfectly in this way ; in fact in some cases it cannot 



