30 



branous bag, and the copper in a surrounding solution of sul- 

 phate of copper, the proportion of zinc to copper was as one 

 to eight, the impediment to the passage of the current being 

 double in the latter case what it was in the former. 



" Fifth Experiment. 



*' Five cylinders of zinc, 10 inches high, ^ diameter, were 

 placed in glass vessels, containing sulphuric acid, as before. 

 Into these were placed cylindrical earthenware vessels, 1^ 

 inches diameter, containing pure nitric acid ; slips of platina 

 foil were rolled into cylinders as before. 



Cubic Inches. 



Time, 2 minutes, 2-0 



After 10 „ .2-5 



„ 30 „ 3-0* 



" From these data may be calculated the heights of the 

 zinc pipes, and the weight of platina foil required to obtain 

 any given decomposition, to be employed, as shewn by 

 Jacobi, either as a motive power, or applied to light-houses, 

 to the polariscope, or to the fusion of refractory substances. 

 For the latter purposes, I had fixed to a strong, shallow 

 woolf bottle, two tubes with glass cocks, and to them tubes 

 containing chloride of calcium, applied to a Daniell's jet, 

 playing upon a cylinder of lime, rotated by clock work. 

 A third tube was inserted in the bottle, intended as a regu- 

 lation of the pressure, or a safety valve, in case of explosion." 



Dr. Apjohn then made a brief verbal communication on 

 the subject of the Composition of Pyrope. This mineral, long 



* " The dilute acid in the voltameter began to boil ; the cause of the increase 

 of decomposition, compared to what took place in the small cylinder, was the small 

 stratum of sulphuric acid between the porous vessel and the zinc. For a continu- 

 ous action the zinc pipes, sealed at one end and amalgamated, should be connected 

 by pipes at top and bottom, with an earthenware vessel, containing the sulphuric 

 acid." 



