356 TRANSACTIONS OF THE 



the two acids change places — the sulphuric acid preferring the ammonia, 

 the carbonic acid the lime. It is not only present in many soils, but is 

 also found in springs which ascend from rocky localities, and in numerous 

 plants. It is extensively employed for the purposes of promoting the 

 growth of vegetable productions. Naturally it contains more than twenty 

 per cent of water, which it loses on being exposed to fire-heat, and is re- 

 duced at once to an impalpable powder ; but if exposed to moisture imme- 

 diately combines with twenty per cent of water, and by a small additional 

 quantity may be poured into a mould, where it becomes a solid mass in a 

 few moments. In this manner burned plaster is employed in the manufac- 

 ture of cornices, busts, &c. Burned gypsum consists of sulphuric acid and 

 lime only, in the proportions of 58| of the former, and 44^ of the latter. 

 Pure gypsum contains : 



Sulphuric acid 43 parts. 



Lime 33 do 



Water 24 do 



too 



In this State there are only four cultivated plants that contain it in 

 sensible proportions, and to which four only it forms a direct food, to wit : 

 clover, rye, grass, sainfoin and lucern ; and, consequently, it will always be 

 found an admirable top-dressing for these. By analysis wheat, barley, 

 peas, beans and oats do not contain a trace of it ; consequently it is not 

 worth while to waste it upon these crops. It has been supposed to possess 

 imaginary powers of absorbing moisture largely from the atmosphere. 



I imagined this to be the case, until, by the following experiment, my 

 error was discovered. I dried five hundred parts of plaster, -and then 

 exposed it four hours in a foggy atmosphere, when it only gained four parts 

 in weight ; while at the same time a portion of good soil, dried and exposed 

 along side of it, absorbed 15 parts, a sample of soot 40 parts, and stable 

 litter 150 parts. Placed in the manure heap it retards putrifaction and 

 rapid decomposition. 



The time selected to spread plaster has a very material influence upon 

 its usefulness. Its effects are rarely apparent when sown in dry weather. 

 The season should be moist, and the leaves of the grasses wet, when the 

 advantage will be immediate. Two hundred pounds to the acre will be 

 generally found suflicient to produce a maximum benefit. If the result is 

 not favorable, and the land good, you may make up your mind that the 

 soil naturally contains a suflicient quantity of this salt, and that something 

 else is required. 



I once had a field that formerly produced splendid crops of red clover, 

 refuse to grow it more than six inches high, and exceedingly sparce at that. 

 Farm-yard manure was spread upon it at the rate of thirty loads to the 

 acre, without adding to its luxuriance. Other enriching substances were 

 placed upon it, still without effect. I analyzed the sub and surface soil, 

 and found it absolutely deficient in sulphate of lime, and immediately sowed 



