164 Lectures on the Besults of the 



monly employed in relation to bodies of like atomic composition, and 

 lias reference to equality of parts. The term allotropism is a better 

 denomination, and lias reference to tliecondition 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 con- 

 tact 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 be- 

 comes 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 inves- 

 tigating 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 em- 

 ploying on aqueous solution of soda, Mr Mercer found that, by pass- 

 ing the solution through the calico, soda was removed. This re- 

 moval 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. 



The result of this agency of soda was, as formerly remarked, a 

 physical corrugation, and an acquisition of certain chemical qualities. 

 The former change was evident to the eye. Dr Playfair exhibited 

 two stockings, one of which being nearly double the size of the 

 other, although both came equal in size from the loom. The 

 difference had been occasioned solely by chemical not mechanical 

 agency. Dr Playfair, in developing the numerous practical appli- 

 cations of this physical effect, shewed that, besides the most ob- 

 vious one of producing a material of increased fineness, the cotton 

 thus prepared was far more capable of being dyed. Hot soda solu- 

 tion would not answer ; and this fact was remarkable, and had its 

 analogue in those salts which deposited themselves anhydrous on 

 boiling. Instead of soda sulphuric acid might be employed ; in 

 which case it formed, in combination with the cotton fibre, an easily 

 decomposable conjugate acid. 



(B.) — Some years ago Liebig stated that one of the greatest dis- 

 coveries of chemistry would consist in converting coal-gas into a 

 solid form, thus enabling it to be burned like a candle. This had, 

 in a manner, been accomplished by Mr Young. About three years 

 since, Dr Playfair drew the attention of Mr Young to a spring of 



