FARMEES' INSTITUTES. 257 



in New York, then found in abundance in our OAvn State, and has since been 

 discovered in many States of our Union. Inexhaustible deposits of this vahia- 

 ble mineral have been discovered in Kansas. According to the last State cen- 

 sus 128,000 tons of plaster were quarried in our State in 1873. If we add to 

 this the amount brought into the State from Ohio and Canada, the value of 

 the plaster yearly used in our State will not fall below half a million dollars, 

 aud probably much exceeds that sum. If any large portion of this plaster is 

 used in such a way as not to yield the best possible results, a very large leak in 

 the profits of farmers of this State will thus be discovered. 



THEORIES OF ACTION OF PLASTER. 



Many theories have been advanced to account for the peculiar value of jjlaster 

 as a manure. Hlubeck gives the following summary of theories which have 

 been advanced on this subject : 



''Acts like any other food." — Ruckert. 



"Merely improves the physical properties of the soil." — Pastor IMeyer. 



"Is an essential constituent of the plant." — Eeid. 



"Gypsum is the saliva and gastric juice of the plant." — Hedwig. 



"It is a stimulant, by which the circulation of the plant is increased." — 

 Humboldt & Thaer. 



"It is an essential constituent of plants, because it acts only when gypsum is 

 deficient in the soil." — Sir Humphrey Davy. 



"It fixes the ammonia of the atmosphere." — Liebig. 



" It furnishes sulphur for the legumin of leguminous plants." — Bracounot & 

 Sprengel. 



Many of these theories are mere fanciful conceits, founded upon analogies 

 drawn from animal life, and demand no very careful consideration at our hands. 

 Others have important tniths, and demand more careful consideration. 



KINDS OF SOIL ON WHICH GYPSUM ACTS BENEFICIALLY. 



All persons Avho have carefully noted the eifects of gypsum when aj)plied on 

 different kinds of soils have observed that on dry, porous, gravelly or sandy 

 soils the effect is much more marked than when applied to stiff, tenacious 

 clay lands, especially when they are Avet or water-soaked. So, also, the influ- 

 ence is more marked in a ratlier dry season than in a very Avet season. The 

 influence of plaster is very little or nothing on a soil destitute of vegetable mat- 

 ter, unless manure is applied in connection Avith the plaster. The presence of 

 a good supply of vegetable matter in the soil I consider to be essential to the 

 best influence of plaster, and if the soil is deficient in vegetable mold, that defi- 

 ciency Avill limit the action of plaster. The use of plaster by itself tends to 

 dissipate the vegetable matter in the soil, and if this tendency is not counter- 

 acted by such a system of cropping as Avill tend to accumulate vegetable matter 

 in the soil, the use of plaster may tend to exhaustion of the soil. Many farmers 

 complain that while plaster at first seemed to benefit their lands, after a while 

 it seemed to have no beneficial effect. This may haA-e arisen from lack of veg- 

 etable matter in the soil. At any rate this is a possible condition Avhich should 

 be borne in mind in the use of plaster. 



COMPOSITION. 



Gypsum or plaster is sulphate of lime, or a union of sulphuric acid (or oil of 

 vitriol) and lime; and contains tAvo equivalents of water of hydration. The 

 percentage composition is nearly as folloAVS : 



33 



