PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 363 



liypothemise side is at an angle of 45** with it. This rhombohcdron surface 

 occupies the axis of the poUirizing' apparatus instead of the Nicol prism. 

 The light thus snfTers two refractions at the equal surfaces, and one reflec- 

 tion at the hypothenuse surface. 



This instrument is said to be well adapted for experiments in the polar- 

 ization of heat as well as ligiit. 



Molecular Structure. 



M. D. Gernez describes experiments made by him on the rotary polarizing 

 power of the essences of turpeiiliiie and camph(jr, from wliich he concludes 

 that when these liquids vaporize, their molecular structure undergoes no 

 change. 



Potash from the Jersey Green Sand. 



i[r. G. J. Scattergood has described a process for extracting 10 or 12 per 

 cent, of potash from the marl or green sand of New Jersey; but this source 

 of potash is not as available as common wood ashes. 



Saltpetre. 



Jf. Boussingault, in describing before the Paris Acadcmj-- of Sciences the 

 Saltpctn; works of Tacunga, remarks that nitrate of potash or saltpetre is 

 spread throughout Nature with astonishing profusion. It is found in rain, 

 snow, hail, dew, fog, and in fresh and salt water. Wherever a body is 

 burnt in the atmosphere, the oxidation of nitrogen and the formation of a 

 nitrate generally takes place. Nevertheless, Nitre is present everywhere 

 only in very small quantities. The places where it is found in abundance 

 are very rare, the only known spot where it attains the proportions of a 

 nn"neral stratum being the Province of Zarapaca in Peru. Whenever it 

 ajipears spontaneously, the diverse circumstances all denote the interven- 

 tion of organic matters. A dry air and long periods with rain are indis- 

 pensable to its formation, also the presence of decomposed feldspar, yield- 

 ing the requisite potash. 



Soda in Coal Gas. 



Prof. Vogal, of Munich, has examined with the spectroscope the coal gaa 

 supplied in that city, and found in tlie spectrum the p«le soda lime, which 

 was not ol)served after the gas had been passed through sulphuric acid. 

 On examining a copper burner which had been in use a year, he detected 

 the sulphate of soda. 



Action of Marsh Gas on Metallic Oxides. 



Jf. Midler has submitted the oxides of Iron, Manganese, Cobalt and Lead 

 to the action of a stream of niarsii gas, which is a combination of two cqm'v- 

 alents of carbon with three of hydrogen. lie found the action of tiie gas 

 was in all cases reducing. As carbon could not be detected in the sub- 

 stances formed, he concludes that at a red iieat the affinity of the metula 

 for liie carbon of the gas is inconsiderable. 



