134 NOTICES OF THE MEETINGS (Feb. 27, 
differ, but their colour and their specific gravity. Thus, the sulphuret 
of iron (Fe. S,), when crystallized in cubes, is persistent in the 
air; but when occurring in a rhombic form, readily passes into cop- 
peras or sulphate of iron. 
Applying the preceding remarks to non-crystallized bodies, it was 
equally found that many were susceptible of allotropic modification. 
Thus cinnabar and vermilion were of precisely similar chemical 
composition with the black sulphuret of mercury. Again, the sesqui- 
sulphuret of antimony might be black or orange. Iodide of mercury 
is commonly red; when heated, however, it passes into a yellow 
powder, which by simple pressure and rubbing with a hard body 
becomes red again. Sugar is a remarkable instance of a solid 
capable of assuming two allotropic states; as sugar candy it is erys- 
tallized, as barley sugar it is amorphous; yet the composition of 
sugar in either case is the same. Nor are liquids exempt from the 
strange state of allotropism,—sometimes indeed manifesting a 
condition even beyond allotropism (‘somerism), and not allowing us 
to reconvert them to their primitive state. Thus the chemical com- 
position of oil of turpentine, of rosemary, of lemons, of copaiba, are 
identical, yet no one of these bodies has hitherto been turned into 
the other. The steroptane of otto of roses is identical in compo- 
sition with coal gas, yet chemists are unable to change one into the 
other. The term isomerism has been commonly employed in rela- 
tion to bodies of like atomic composition, and has reference to 
equality of parts. The term allotropism is a better denomination, 
and has reference to the condition of unlike properties. 
The preceding remarks by Dr. Playfair were introductory to an 
exposition of the respective discoveries of Mr. Mercer, Mr. Young, 
and Dr. Schrotter. 
A.— Mercer’s process consists in bringing cotton fabrics in contact 
with a solution of soda (cold), or a solution of dilute sulphuric acid, 
by subjecting it to either of which processes cotton acquires certain 
remarkable properties. In the first place, the texture becomes very 
much corrugated, and hence proportionably finer; it also assumes 
acid properties, rendering it more capable of taking up dyes. The 
process of induction which led Mr. Mercer to his final discovery was 
curious. He started from the point of investigating the laws which 
determined the flow of water at various temperatures through minute 
tubes. From water he proceeded to aqueous saline solutions; from 
tubes he proceeded to their equivalent, namely, closely-folded woven 
tissue. Selecting for this purpose a thick reduplication of calico, 
fold on fold, and employing an aqueous solution of soda, Mr. Mercer 
found that, by passing the solution through the calico, soda was 
removed. This removal he attributed to the act of filtration; but, 
subsequently finding that mere immersion of the calico in the same 
solution effected a like result, he concluded that the result was due 
to an actual combination of the cotton with the soda—a calico-ate 
of soda (if the lecturer might be permitted that form of expression) 
was generated, 
