CHAPTER XVI. 



Experiments with the compounds of baryta and alumina, and with burned clay 

 and shale. Experiments with sulphate of baryta, sulphuret of barium, and 

 carbonate of baryta. Suggestions for experiments with sulphate of alumina, 

 and with common alum. Experiments with burned clay. What are the 

 qualities which fit a clay for burning ] Mechanical and chemical effects of 

 burning upon a clay. How it afterwards acts when laid upon the soil. Sug- 

 gestions for comparative experiments with burned clay. Experiments with 

 bituminous and other shales burned and unburned. 



1. Experiments with sulphate of 'baryta, with sulphuret of 

 barium, and with carbonate of baryta. 



1. The sulphate. When treating of the uses of gypsum, I 

 mentioned sulphate of baryta as having been tried to a small 

 extent in comparison with it, and with a view to theoretical 

 inquiry I recommended that farther comparative experiments 

 should be made with this substance, (see p. 128.) In some 

 localities this sulphate occurs in veins of considerable thickness, 

 and may be procured at a comparatively cheap rate. 



2. The sulphuret. When the sulphate of baryta is mixed 

 with charcoal, and heated to redness in a close crucible, it is 

 deprived of its oxygen, and is converted into sulphuret of 

 barium. This compound dissolves readily in water, and gives 

 a solution possessed of a yellow colour and a sulphureous taste 

 and smell. In regard to this substance, I find it stated that 

 Mr Chapman of Pennsylvania tried it as a manure, and found 

 it to " exceed gypsum in its effects^ not only on dry gravelly 

 lands, but also on clays. It expelled insects from his garden, 

 and he considered it the most powerful manure ever yet dis- 

 covered."* I have not formally recommended any trials to be 

 made with sulphurets in the previous chapters of this work. 

 In the case of substances like this sulphuret of barium, however, 

 * NICHOLSON'S American Farmers Assistant, 1820, p. 221. 



