EFFECTS OP GYPSUM. 115 



previously explained under lime, some physical or 

 chemical defect which prevents their action. 



Gypsum, before it is burned, consists of sulphuric 

 acid, lime, and water; of the latter, there are about 

 21 lbs. in evti V ' ' J. This water can be easily 

 driven off by ;. iie ground gypsum. This may 



be done with a small quantity, by way of experiment, 

 over a common lamp. During heating, it whitens : 

 it is this burned gypsum that is used for the cornices 

 of rooms, for making casts, for hard finish, etc When 

 water is mixed with it, a considerable degree of heat 

 is produced, the 21 per cent of water is again ab- 

 sorbed, becoming once more a part of the solid stcme, 

 and tlie whole mass hardening or setting, as it is 

 termed, in a few moments. It is upon this property 

 of hardening when mingled with water, that the ums 

 of gypsum in the arts, as above mentioned, depend. 



This manure frequently proiluces a most beneficial 

 eflT... t vt},en applied as a top dressing upon pastures 

 > i'>ws : it is also a favorite and excellent appli- 



cauuu lu young corn and potatoes. It is of service 

 not only Gy tht- valiial)lf nutriment which it furnishes 

 to the plant, I from a cirtain power which it 



posscssi-ji of a. moisture and gases. 



a. Liebig ha» supposed that much ^'cct iqpOB 



grassland is owiiitr to this propert). i attraeftl 



ammonia from th< .«re, and retains it for dM 



use of plants. Ti..^ ... without doubt an importaat 

 effect, but should not be conaidered the principal on*. 



b. To this same i be ascribed its actioA 

 when scattered o. heaps, or mixed 

 the liquid in tanks. la both cases it absorbs 

 nia, and prevents its escape. \\Tiitc fumes d i 

 nia may sometimes be ; v the ejn md 



the sense of smeU, risiu^ ...^ ^......c of icrmcnt- 



ing manure heaps. A little gypsnm sprinkkd ovw 



l^ysiiri'a' '■ •*■" '■ vill arrest this ev a poc ti ai 



and loss v. 



