CHEMISTRY. 275 



ON THE FORMATION OF SALTPETRE IN CAVES. 



At a recent meeting of the Boston Society of Natural History, Professor 

 "William B. Rogers remarked that, from his observations in the caves of the 

 Middle and Southern States, he was satisfied that the earthy deposit contain- 

 ing the nitrates, known hi some places as Petre dirt, was chiefly derived from 

 the overhanging and adjacent rocks, and not from sediment brought into the 

 cave by existing or former streams. The limestone, in which the nitriferous 

 caverns are found, often contains a large amount of siliceous and argillaceous 

 matter, and, hi some instances, a marked proportion of organic substances. 

 The more pervious layers, gradually deprived of their carbonate of lime by 

 the leaching action of the water infiltering from above, are reduced to an 

 earthy mass, the mere caput mortuum, as it were, of the original rock. In 

 some cases this decomposition pervades the stratum for a great distance ; the 

 residuary, fine grained, ashy clay retaining the lamination and bedding which 

 it had before the change. In course of tune the earthy mass falls to the 

 floor by its own weight, aided, perhaps, by occasional tremors of the ground, 

 or is detached by the load of stalactites suspended from it below, and thus 

 comes within the levelling and transporting action of the streams flowing 

 through the cave. 



As to the production of the nitrates with which the Petre dirt is more or 

 less impregnated, Professor R. thought that it could not, in any large degree, 

 be referred to the excretions and other remains of animals occasionally found 

 in these caves ; since the quantity of nitrogen required for this purpose would 

 far exceed such a means of supply. Besides this, the nitrates are found in 

 the earthy mass while it is still adhering to the roof or walls, and far removed 

 from the organic matter supposed to be buried in the floor. ISTor can we 

 regard the nitrogen as chiefly derived from organic substances in the decom- 

 posing rocks. For in the case of some caves producing Petre dirt, the sur- 

 rounding limestone contains only a trace of such ingredients. We must, 

 therefore, refer the formation of the nitric acid, and ultimately the nitrates, to 

 mutual chemical reactions between the porous calcareous earth and the con- 

 tiguous atmosphere. 



ANTIMONIAL YEEMILLION. 



M. E. Plessy has invented a process for preparing vermiUion, of a beautiful 

 color, of antimony and sulphur, and which process is sufficiently simple to 

 admit of preparation on an extensive scale. 



The first ingredient necessary for the manufacture, hyposulphate of soda, is 

 prepared as follows : In the upper part of a vessel, the bottom of which is 

 broken out, a sieve containing large crystals of carbonate of soda is fixed. 

 Into the lower part of the vessel projects a furnace pipe bent at right angles, 

 which is attached to a small clay furnace. Into this furnace sulphur is thrown 

 by little and little, and burns into sulphurous acid, which passes through the 

 tube into the vessel, and there acts upon the carbonate of soda. The com- 

 bustion of the sulphur may be regulated as occasion requires through the 

 door of the furnace ; the draft is quite sufficient, and hi the course of three or 



