CHEMICAL SCIENCE. 261 



of the fossils, while the sulphate of lime formed by this reaction has been 

 accumulated often in large groups of selenite crystals in the lower and com- 

 paratively impervious layers. In many cases, the residuary sulphuric acid, in 

 the presence of much diffused organic matter, has been wholly deprived of its 

 oxygen, and reduced to the condition of sulphur, so that, over wide areas, 

 these ancient, and now effete marl beds, exhale a sulphurous odor, and yield 

 a sensible amount of sulphur when exposed to heat in a close vessel. 



Professor Rogers then referred to the acid and alkaline springs of the slate 

 formations of the Appalachian belt, as depending on the development and re- 

 actions of sulphuric acid. The former class of springs, always containing an 

 excess of this acid, along with earthy and other sulphates, were observed to 

 originate in belts of slaty rock, containing no carbonate of lime, either diffused 

 or in the shape of interpolated layers. The latter issued from slates rendered 

 more or less calcareous by the presence of fossil shells and plates of limestone. 

 The sulphuric acid evolved by the oxydation of the iron pyrites abounding in 

 both these varieties of slate remained, in the former case, in part uncarbonized. 

 and was carried off by the waters of the so-called Alum Springs; but in the 

 calcareous slates the effect was different. Here, reacting with the carbonate 

 of lime, it became neutralized, and, at the same time, set free an immense 

 amount of carbonic acid. This agent, favored probably by pressure due to 

 depth, as well as by relative quantity, dissolved out a portion of the carbon- 

 ates of lime and magnesia of the slates, and by reacting on the salts of soda, 

 always present, formed the carbonate of that base. The percolating water 

 thus became impregnated with earthy and alkaline carbonates, and with an 

 unusual amount of silica due to the solvent action of the latter, and in this 

 way, as he conceived, were formed the well-known alkaline springs of these 

 slate regions. 



OBJECT OF SALT IX THE SEA. 



Professor Chapman, University College, Toronto, has published an interest- 

 ing paper on the object of sea-water being salt, and after giving his objections 

 to the usually received opinions, he urges the theory that the object is to 

 regulate evaporation. If any temporary cause renders the amount of saline 

 matter in the sea above its normal value, evaporation goes on more and more 

 slowly. If this value be depreciated by the addition of fresh water in undue 

 excess, the evaporating power is the more and more increased. He gives the 

 results of various experiments in reference to evaporation on weighed quanti- 

 ties of ordinary ram- water, and water holding in solution 2*6 per cent, of salt. 

 The excess of loss of the rain water compared with the salt solution was, for 

 the first twenty-four hours, 0*54 per cent. ; at the close of forty-eight hours, 

 1-04 per cent; after seventy-two hours, T46 per cent, and so on in increas- 

 ing ratio. 



APPLICABILITY OF GELATIXE PAPER FOR COLORING LIGHT. 



This material was invented hi 1829, but up to the present time has not been 

 successfully applied to any more useful purposes than the manufacture of ar- 



