PROCEEDINGS OF THE CHEMICAL DEPARTMENT. 503 



out that one of the most important considerations is to obtain 

 a means of determining not only the total quantity of any sub- 

 stance that exists in a soil, but also its different states of combina- 

 tion, so as to discriminate between those portions which the plant 

 can easily obtain and assimilate, and those which are, as it were, 

 locked up in an inaccessible condition. Hitherto chemists have 

 divided the soil constituents into those soluble in water, those 

 insoluble in that fluid but soluble in hydrochloric acid, and those 

 insoluble in both menstrua. The latter, it has been supposed, 

 and apparently with justice, are at this moment entirely inac- 

 cessible to plants, though they may, in the course of time, be- 

 come accessible, by virtue of those changes constantly induced 

 by the action of air and moisture. On the other hand, it has 

 been supposed that the portion soluble in water must be the 

 most readily available, and the portion soluble in hydrochloric 

 less so, though still capable of assimilation. 



The recent researches of chemists on the absorptive power of 

 soils and allied subjects, which show that plants can and do take 

 a great part of their food from the portion of the soil insoluble 

 in water, has diminished the importance of the soluble part ; 

 while other experiments tend to show that of the part soluble in 

 hydrochloric acid, a portion, and in some cases a very large 

 portion, may be unavailable. With the intention of making a 

 further distinction between the different states in which the 

 constituents of the soil exist, I last year introduced the use of 

 acetic acid as a solvent, supposing that that feeble acid would 

 give, in the portion it dissolved, an indication of the amount 

 of very accessible matters in each soil. The first impression I 

 derived from these analyses was not of a very favourable cha- 

 racter; and therefore, when the analyses for 1867 were com- 

 menced,- I resolved to omit what is a very troublesome and 

 laborious part of the analysis, and returned to the old plan. 

 More mature consideration has led me to doubt as to the propriety 

 of this ; and I now think that the information derived from the 

 composition of the acetic solution was greater than at first 

 supposed, and I therefore regret the omission, which it is now 

 too late to supply. 



With this exception, the analyses were conducted in the same 

 manner as last year. As the process, so far as necessary, was 

 described in the Transactions then, it is unnecessary to revert to 

 it here. I must only mention that the quantity soluble in hydro- 

 chloric acid includes also that soluble in acetic acid. 



SOIL FROM MR DOVE, ECCLES NEWTON. 



This was a soil of fair quality, but rather light, and containing 

 but a small quantity of clay. It was pale in colour, and judging 

 from the small pieces of rock it contained, appeared to be formed 



