On Gypsum, 169 



country. From its cradle, it has had my assistance, to 

 foster and rear it. — Now, it is of full age ; and has gain- 

 ed strength and solidity of character, sufficient to sup- 

 port itself. Knowing exactly its origin, and the preju- 

 dices attending its infancy, I see with some surprize, 

 but more satisfaction, the state of perfection and matu- 

 rity, to which it has grown up. So that it is now^ not 

 only an important branch of commerce and manufac* 

 ture ; but a general, and essential requisite in agricuU 

 turCo 



Additional Observations on Plaister oj* Paris* 



In exhausting this subject so far as my imperfect 

 stock of information or conjecture enables me, I fear I 

 shall exhaust also the patience of the society unprofit- 

 ably. 



I have been frequently asked '' what quantity of plais- 

 ter an acre of ground requires f^"^ No precise answer can 

 be given to this question. It depends on the quantum 

 of substances in the earth, on Avhich the component 

 parts of the gypsum operate, or are by them operated 

 upon. As these are in plenty or scarce, the effects are 

 produced in a greater or less degree. And when they 

 are exhausted, or where they do not exist, no quantity 

 of gypsum, will produce agricultural benefits. If there 

 be a greater quantity than is required to exhaust the 

 subjects of its operation, the excess will remain an inert 

 mass ; inactive till new subjects call forth its powers. 



The theory I long since mentioned, (with no small 

 diffidence as to its chymical accuracy) has been uni- 

 formly useful, and practically efficient. Dr, Priestley^ 



•K k 



