Dr. Playfair’s Lecture on the Great Exhibition of 1851. 27 
treated, it contracts to calico of 260 picks to the inch—a fineness 
not yet attained by any mechanical contrivance, This calico, in 
addition to its acquired fineness, has also assumed powers which 
enable it to receive colors superior to those assumed by ordinary 
calico. Before leaving this important discovery of Mercer, I 
should allude to one other by the same chemist. 'The French 
ealico-printers employ mousselines-de-laine consisting altogether 
of wool, while in England we use a much cheaper fabric, con- 
sisting of wool and cotton. The colors of this mixture are, 
however, extremely meagre when compared with the former; 
but Mercer has shown that the mixed fabric acquires the proper- 
ties of the other, when it is treated with a bath of chlorid of 
lime. ‘This, one of the most important discoveries ever made in 
calico-printing, has been of great value to this country. 
€ 
its fixation was a real difficulty. Chemists suggested that the 
ultramarine might be mixed with albumen, which, being coagu- 
lated by heat, would retain the color on the cloth to which it was 
applied. Whole barrels of the dried white of eggs are now to 
be seen at calico-print works. Yet this is an expensive process. 
Could common cheese not be substituted for the white of eggs? 
Cheese is soluble in ammonia, and the ultramarine, being mixed 
With this solution, is retained by the cheese, when the ammonia 
evaporates. Now, therefore, the ultramarine is fastened on by 
cheese, made from the buttermilk of Scotland, and sold under 
1¢ name of lactarine. 
