242 FERTILIZERS. 



sulphuric acid ; or, the hydrous gypsum is composed of sulphate of lime 79 • 2, and water 

 20 - S. The latter is: the species of gypsum employed in agriculture. It is met with under 

 a variety of forms, as in transparent lamina called selenite, and not unfrequently considered 

 as isinglass, and regarded as worthless ; also in columnar forms, both fine and coarse, and 

 of a variety of colors. The common form is that of a coarse gray rock, with a fine granular 

 texture, and destitute of lustre or beauty. The rock is easily recognized from all other 

 rocks by its softness, except some of the magnesian rocks, as soapstone, steatite or talc. 

 The geological position of a rock suspected to be gypsum will often be sufficient to deter- 

 mine the fact whether it is this substance or not. Thus gypsum never occuis in primary 

 rocks, or in any way is it associated with them ; hence any specimen which is known to have 

 belonged to a primary district, furnishes sufficient evidence against its being gypsum. In 

 New-York it occupies a certain geological position among its sedimentary deposits, though 

 gypsum occurs elsewhere in the sedimentary series in other sections of the country. Gypsum 

 is tasteless ; it is sparingly soluble in water ; 400 grains of water dissolving one grain of 

 the mineral. The history of gypsum as a fertilizer is interesting on more accounts than one : 

 it shows on what slender grounds a valuable substance is opposed ; sometimes the opposition 

 arose from selfishness alone, as noticed by Boussingault ; in other instances the friends of 

 gypsum injured their cause by exaggeration of its value and effects. It was often regarded 

 as a universal improver of soils, and capable of supplying the place of all other substances : 

 experience, however, in time, proved the contrary, and it has happened, as in many other 

 instances of a like kind, reaction followed, from which its properties were as much under- 

 rated as they had been before exaggerated, by its friends. Besides the unfavorable influences 

 growing out of misrepresentation, there were substantial facts which militated against gypsum 

 though they were rather of a negative character. It was found, by experience, that there are 

 some crops upon which gypsum failed to produce perceptible influences ; and there were, too, 

 conditions accompanying its application, which also rendered it inert and useless. Thus it 

 was proved, and it is confirmed by modern experience, that it does not operate usefully upon 

 wet meadows ; neither does it increase the product of wheat when directly applied to it. Be- 

 sides the foregoing facts of an unfavorable charcter, there are sections of country upon which 

 it never operates decidedly at all ; Long-Island, for example. The testimony in regard to its 

 use is generally of a negative character; and it is quite difficult to assign a reason for its 

 general failure here, though it has been supposed, by some, that there is in the soil a sufficient 

 amount of gypsum to answer the purposes of vegetation, though it is not established by analysis. 

 So it has been maintained that proximity to the sea renders it inert : but the proximity to the 

 sea is only a fact which, when really scanned, can have but a remote bearing on this question, 

 unless it can be proved that lime, in some way or other, may be derived from a marine at- 

 mosphere. There are instances upon Long-Island, however, where gypsum has operated fa- 

 vorably, and hence the proximity of the sea is not always operative as a preventive. 'The 

 probability is, in the case of Long-Island, there are other elements wanting in the soil besides 

 lime or gypsum ; and hence, as it is incompetent to supply those other substances which are 



