68 



Prof. J. Dewar on the 



[Mar. 15, 



7*37 cubic centimetres. 



An absolute determination of the nitrogen was made with the follow- 

 ing results : — 



"Weight of acid taken 0-1087 gram. 



Volume of nitrogen at 0° C. and 1 

 760 millimetres pressure .... J 



Weight of nitrogen -0092 gram. 



This gives the percentage of nitrogen as 8*5 instead of 7*8, as required 

 by theory. The acid used in this experiment was not quite pure, and 

 the quantity taken too small for an accurate determination. 



Equivalent of the Acid. — A quantity of the acid, weighing 0'445 gram, 

 titrated with pure caustic soda solution, every 1*73 cubic centimetre of 

 which contained 23 milligrams of sodium, required 4-28 cubic centi- 

 metres of this solution to neutralize the quantity of acid taken. Hence 

 the equivalent of the acid is 179. 



Professor Liveing has kindly determined the following crystallographic 

 constants : — 



Pig. 1. 



"The acid crystallizes from 

 solution of ether in tufts of thin 

 plates which show the form of 

 fig. 1. 



" The face a is the only one 

 which is largely developed. They 

 cleave readily in plane c at right 

 angles to a. The faces 6, b' are 

 equally inclined to a, their nor- 

 mals making an angle of about 

 53° with that of a. The normals 

 to b, c make an angle of about 

 69°. The normal to face d is in- 

 clined to that- of a at about 42°. 



" Many of the crystals do not 

 show the faces d, but are termi- 

 nated by faces parallel to c. Some 

 show some smaller facets at the 

 apex, barely discernible. 



" There are occasionally twin 

 crystals, with the twin face pa- 

 rallel to the edge b and at right 

 angles to a. 



" The crystals appear to be- 

 long to the oblique prismatic 



system, with the inclined axes in a plane parallel to a. 



" The uncertainty about the measurements is due to the minuteness of 

 all the faces except «, and will perhaps be overcome when a fresh crop 

 of crystals is obtained." — Gr. D. L. 



