62 



Scientific Proceedings, Royal Dublin Society. 



gravity is required. The vaseline completely encloses all of the 

 powder. The pan and its contents may now be cooled, and again 

 weighed in water. Let this weight, viz. of the pan and the vase- 

 line and the powder, be tv 2 ; then w % - u\ is the weight in water of 

 the quantity of powder used. If the weight of the powder used 

 be TP, then W - (w s - Wi) is the weight of water displaced by 



W 



the powder, therefore its specific gravity = — — — -. 



Evidently the specific gravity of the vaseline does not come into 

 the result. As regards the accuracy of the method, I add the 

 results of some of the determinations which I have made with it. 



The first column gives the weight in grammes of the substance 

 used. In the second are the values which I have found, and in 

 the third the corresponding values given by Naumann. 



* This specific gravity is apparently low for quartz, but the powder, when 

 examined under the microscope, was seen to be very full of air bubbles. 



