12 A Tribute to the Memori) of 



a specific epithet should be added, to distinguish each particu- 

 lar variety. In this essay Mr. Henry, for the first time, ex- 

 plained the true nature of the liquor which is employed for af- 

 fording the aluminous basis, prepared by mixing the solutions of 

 alum and of sugar of lead. This liquor he shewed to be essentially 

 a compound of pure clay or alumine with acetic acid ; and its 

 superiority over a solution of common alum, for yielding the 

 earthy base in dyeing, he ascribes partly to the less affinity of 

 the acetic acid, than of the sulphuric, for alumine, and partly 

 to the greater volatility of' the acetic acid, when exposed to a 

 moderate increase of temperature. The remainder of the paper 

 is chiefly occupied with the details of the operations then prac- 

 tised for dyeing Turkey red ; with a theory of the process, and 

 with a general view of the mode of action of the individual mor- 

 ,dants or bases. The methods of dyeing Turkey red have been 

 since much improved and simplified, though its theory is, even 

 yet, far from being well understood. But the opinions incul- 

 cated by Mr. Henry respecting the action of mordants, evince a 

 remarkable superiority to the prejudices with which he found the 

 subject encumbered, and are indeed those which are still held by 

 the latest and best writers on the principles and practice of dyeing. 

 In the year 1783, an institution arose out of this society, 

 Avhich had great merit, not only in its plan and objects, but in 

 the ability exerted by the several persons, who were concerned 

 in their fulfilment. It was destined to occupy, in a rational and 

 instructive manner, the evening leisure of young men, whose 

 time, during the day, was devoted to commercial employments. 

 For this purpose, regular courses of lectures were delivered on 

 the belles lettres, on moral philosophy, on anatomy and physio- 

 logy, and on natural philosophy and chemistry. Mr. Henry, as- 

 sisted by a son, whose loss he had afterwards to deplore, and 

 whose promising talents and attainments obtained for him, at an 

 early period of life, a mark of the approbation of this Society*, 



* See Dr. Percival's eloquent address to Mr. Thomas Henry, junior, 

 on prescntingto him the silver medal of the Society.— Mew(o»v. of the So- 

 ciety, Vol. JI. page 513. 



