C 



deposited as the water cools. Gypsum is easily dis 

 tinguished when dissolved by its properties of afford- 

 ing precipitates to solutions of oxalates and of barytic 

 salts. 



Great difference of opinion has prevailed amongst 

 agriculturists with respect to the uses of gypsum. It 

 has been advantageously used in Kent, and various 

 testimonies in favour of its efficacy have been laid be- 

 fore the Board of Agriculture by Mr. Smith. In 

 America it is employed with signal success ; but in 

 most counties of England it has failed, though tried 

 in various ways, and upon different crops. 



Very discordant notions have been formed as to 

 the mode of operation of gypsum. It has been sup- 

 posed by some persons to act by its power of attract- 

 ing moisture from the air ; but this agency must be 

 comparatively insignificant. When combined with wa- 

 ter it retains that fluid too powerfully to yield it to the 

 roots of the plant, and its adhesive attraction for mois- 

 ture is inconsiderable ; the small quantity in which it 

 is used likewise is a circumstance hostile to this idea. 



It has been said that gypsum assists the putrefac- 

 tion of animal substances, and the decomposition of 

 manure. I have tried some experiments on this subject 

 which are contradictory to the notion. I mixed some 

 minced veal with about 1^0 part of its weight of gyp- 

 sum, and exposed some veal without gypsum under 

 the same circumstances : there was no difference in 

 the time in which they began to putrefy ; and the pro- 

 cess seemed to me most rapid in the case in which there 

 was no gypsum present. I made other similar mix* 



