254 EXPERIMENTS WITH BARYTA 



of which only the sulphur, so far as we know, can be of any 

 use to the plant, trials on different crops and soils may be made 

 with the prospect of obtaining from them useful information. 

 They will not only test the statements of Mr Chapman, but 

 may throw light upon the economical value of such applications, 

 and upon the way in which sulphur acts in directly influencing 

 the growth of plants. 



3. The carbonate of baryta occurs in some of our mining 

 districts in considerable quantity, and is sold at the rate of a few 

 pounds a ton. It possesses general properties which resemble 

 those of carbonate of lime. But baryta is not found in plants, 

 and cannot, therefore, like lime, directly benefit them by yield- 

 ing what is necessary to form their substance. It would, there- 

 fore, be interesting to ascertain by actual trials, on a small 

 scale, what influence an application of carbonate of baryta 

 would have upon the fertility of the soil in comparison with 

 carbonate of lime. Whatever effect it might have for good 

 would most probably be due to an action exercised on the con- 

 stituents of the soil alone, while, if vegetation were injured by 

 it, the injury might arise from the baryta being actually 

 absorbed by the roots, and acting as a poison on the plant.* 



2. Suggestions for experiments with sulphate of alumina, and 

 with common alum. 



Alumina, like baryta, is not as yet recognised to be a neces- 

 sary ingredient in our cultivated plants. It occurs in the club- 

 moss (lycopodium) and probably in some other plants in sensible 

 quantity, but in those which are grown for the food of man 

 and of our domestic animals it has not hitherto been proved to 

 be necessarily present. This absence of alumina from the plant 

 cannot arise from its scarcity in the soil since of nearly all 

 soils it forms a very considerable proportion. It is rather to 

 be regarded as an arrangement of nature, by which alumina is 

 caused to give tenacity to soils, and a firmer hold to the roots, 

 while the latter are so organised as not to absorb the alumina 

 in any sensible quantity. 



* As to the possibility of such absorption, see the author's Lectures on Agri- 

 cultural Chemistry and Geology, second edition, p. 125. 



