Mb. Crum an the Manner in whkh Cotton tmites with Colouring Matter. 103 



solution in alkalies. Cotton wool has the samo power, and it is exten- 

 sively used, as a means of dyeing with the yellow and red chromates 

 of lead. If lime in excess bo added to sugar of lead, dissolved in a 

 considerable quantity of water, the lead which precipitates is redis- 

 solved in the lime water, and forms a weak solution of plumbate of 

 lime. If a piece of cotton be immersed in this solution, it appropriates 

 the lead, and when afterwards washed and dipped in a solution of 

 chrome, the lead becomes chromate of lead. 



The samo force enables cotton to imbibe basic salts of iron and tin by 

 immersion in certain solutions of these metals ; and many other examples 

 of what Berzelius calls a catalytic force, in decomposing weak com- 

 binations, will occur to those who are familiar with the art of dyeing. 



It appeared to mo interesting to compare the amount of surface 

 exposed by cotton wool, with that of the more minute divisions of 

 charcoal. I am enabled to give the following calculations through 

 the kindness of Professor Balfour, who has furnished me with the 

 necessary microscopic observations. The fibre of New Orleans wool 

 varies most commonly from y^^^ to 2(y\TU ^^ ^^ ^^^^ ^^ diameter. 

 About 40 of these fibres or tubes compose a thread of No. 38 yam, 

 (38 hanks to the pound.) Ordinary printing cloth has, in the bleached 

 state, 493 lineal feet of fibre, or 10*6 square inches of external surface 

 of fibre in a square inch, which weighs nearly 1 grain. It is easy to 

 compress 210 folds of this cloth into the thickness of one inch. It 

 has then a specific gravity of 0*8. One cubic inch has 94163 lineal 

 feet of tube, and 16-8 feet of external, surface; or, if we include the 

 internal surface, there are upwards of 30 square feet of surface of fibre 

 in one cubic inch of compressed calico. The charcoal of boxwood has, 

 as we have seen, 73 square feet of surface to the inch, with a specific 

 gravity of 06. 



Explanation of the Plate. 



It is copied from the paper of Mr. James Thomson on the Mummy 

 Cloth of Egypt, Philosophical Magazine, June, 1834. The drawings 

 were made, at Mr. Thomson's desire, by Mr. Bauer of Kew, the most 

 accurate delineator of microscopic objects that has ever appeared. 

 The figures represent y^^ of an inch in length, and are magnified 400 

 times in diameter. 



A. Fibres of the unripe seed of cotton. In that state the fibres are 

 perfect cylindrical tubes. At * is a fibre represented as seen under 

 water, showing that the water had gradually entered, and enclosed 

 several air bubbles ; proving the tube to be quite hollow and without 

 joints. If separated from the plant in the unripe state, these fibres 

 do not afterwards twist. 



B. Fibres of ripe cotton, both before and after the bursting of the pod 

 or capsule. 



C. Various fibres of unravelled thread of manufactured cotton. 



