GYPSUM— GAS-LIME. 553 



respect would probably require in the case of rich manure 

 nearly 1 cwt. of it to every ton — a quantity much greater than 

 is generally used, though 30 cwt. and upwards per acre have 

 been recommended by some writers. 



M. Mene, however, says, that from numerous experiments 

 he arrives at the following conclusions : — 



1. That gypsum has by itself no fertilising power, and is 

 useless as a manure if employed alone. 



2. That gypsum is only useful when mixed with substances 

 containing ammonia ; in which case there is a double decom- 

 position, and the ammonia is stored up for the use of the 

 plants. 



3. That for gypsum may be substituted any other salt which 

 will fix ammonia, and render it not volatile at the ordinary 

 temperature. 



Gas-lime, or " Blue Billy," a substance poisoaous to plants, has been 

 oooaaionally employed incautiously as a manure, because it contains a 

 large quantity of foetid matters wMcb bave been tbougbt to be beneficial. 

 Manufacturers of fraudulent Guano employ it to scent tbeir worthless 

 compounds. Dr. Ure, speaking of this substance, says, it " contains and 

 easily affords so much of the cyanic compounds that an eminent Parisian 

 chemist has taken out a patent in France for manufacturing prussic 

 acid and Prussian blue from that refuse. The only obstacle to the 

 profitable working of this patent is the accompanying sulphurets, which 

 discharge a great deal of sulphuretted hydrogen, along with the vapour 

 of prussic and sulphooyanio acids ; an aerial mixture of the most intense 

 malignity to breathing animals." And he goes on to say that "that 

 vile refuse should be buried many fathoms deep in some barren region, 

 for when spread on the farmer's field, after discharging the above 

 gaseous poison for some time, its sulphiir gets oxygenated into sulphur- 

 ous acid, two volatile products alike detrimental to plants." Without 

 going into the chemistry of the subject, it is sufficiently obvious that 

 fresh gas-lime is a dangerous agent, wholly unfit for use in confined 

 places. 



It must not, however, be therefore inferred that gas-lime is worth- 

 less or dangerous when properly applied. Its deleterious qualities 

 disappear upon exposure to the air ; sulphuretted hydrogen and 

 sulphurets are speedily decomposed by contact with air and moisture ; 

 and any other pernicious matters which it may originally contain 

 disappear, or enter into harmless combinations. Gas-lime is therefore, 

 when old, a good calcareous manure, fit for the purposes iu which Ume 

 is required — and something more ; for the sulphur-compounds which it 



