Mr. Crum on the Analysis of Nitrates, and on Explosive Cotton. 163 



Tliis important practical consideration had escaped all the men of science 

 that had previously investigated the same subject. 



Professor Gordon gave an account of the viscous theory of Glaciers, 

 illustrated by models and drawings from Professor Forbes. 



XXVI. — Analysis of a Slag, from a Lime-kiln. By Mr. John Brown. 



This Slag presented itself in the form of a congeries of black fused 

 masses, with a resinous fracture, in a lime-kiln at St. Kollox. It dissolved 

 in acids, and gelatinised on evaporation. Its composition was found to be 



Experiment. Atoms. Calculated. 



Silica, 3647 7 38-62 



Lime,.... 28*89 3 28;96 



Protoxide of Iron, ...12-68 1 1379 



Alumina, 18'88 3 18*62 



9692 100-00 



It consists approximately of simple silicates, with an excess of silica, the 

 formula being — 



FeO SiO + 3 (CaO SiO) + 3 (AlO SiO.) 

 The powder emitted a few bubbles of gas when heated with an acid. 



7 th April, 1847. — The Vice-President in the Chair. 



Dr. Nicol made an oral communication on the relation of the science of 

 Astronomy and Geology. 



lAth April, 1847. — Mr. Liddell in the Chair. 

 The following paper was read : — 



XX VII. — On a Method for the Analysis of Bodies containing Nitric Acid, 

 and its application to Explosive Cotton. By Walter Crum, Esq., F.R.S. 



At the first meeting of the present Session of the Philosophical Society, 

 I gave an account of some experimental inquiries into the nature of gun- 

 cotton, a body whose composition was then little known. I had at that time 

 chiefly occupied myself with its nitrous contents, and described a method 

 by which some approximation could be made to a quantitative result for 

 nitric acid. On resuming the subject, I found that much was wanting to 

 render the method a rigorously accurate one; and I shall now relate 

 what I have since done to simplify and complete it. I shall first, however, 

 give an account of its application to nitrate of potash, — a body of known 



