CHEMICAL SCIENCE. 245 



become soluble in the above reagent. He arrived at an analogous result by 

 keeping the cellular tissue of pith for twenty-four hours in boiling water. 



Furthermore, he has remarked that this change takes place only in the or- 

 ganic substance of the tissue; for the proportion of mineral matter remained 

 the same in both cases, and the tissue which had become soluble in the 

 cupreous reagent left, after its calcination, a mineral network, reproducing 

 exactly the form of the vegetable cellules, which same thing happens to tis- 

 sues not modified by either dry or humid heat. 



In order to distinguish between these two kinds of cellulose, Fremy calls 

 para-cellulose that which does not dissolve immediately in the cupreous re- 

 agent. He reserves the name cellulose for that which dissolves directly with- 

 out prevkms treatment. Cellulose is found in cotton, fibres of bark, cellular 

 tissue of fruits or of roots. Para-cellulose constitutes principally the pith of 

 trees, ligneous fibre, the cellular tissue of the epidermis, etc. 



This is not Payen's opinion. The experiment of Frcmy, quoted above, does 

 not appear to him to prove that the pith of the elder is of an isomeric com- 

 position with the cellulose of textile fibres; foi - , in Payen's view, it is not 

 only the fact that foreign substances, in the form of incrustations, oppose 

 the solution of the cellulose in Schweitzer's reagents, but infinitely minute 

 bubbles of air, which are condensed there, have the same effect, to a certain 

 point, in forming a protective envelope. According to him, the pith of the 

 ^Eschynomene, insoluble in Schweitzer's reagent, becomes soluble in it by 

 keeping it in a vacuum in the cold under an exhausted receiver, and after- 

 wards plunging it underwater; the liquid is then placed in a refrigerating 

 mixture. After congealing, the pith has become to a great extent soluble; 

 there remains a residue of fort}' -three per cent., containing fifteen per cent, 

 of mineral substances. These mineral substances, according to Payen, pi*e- 

 vent the complete solution of the cellulose. The same is the case with cor- 

 tical fibres before their purification; so, also, hemp just obtained from the 

 flax-plant, resisted solution for more than six hours, and the portions not 

 dissolved preserved their fibrous form. 



Incrusting Matter Dead Cotton. All these questions have recalled atten- 

 tion to an old paper by Mitscherlich, on the composition of vegetable cel- 

 lules, cellules essentially formed of cellulose, and of a substance analogous 

 to cork, a suberic material, capable of yielding suberic acid, and also suc- 

 cinic and nitric acids. The most delicate vegetable fibres are covered over 

 with this slender coating of suberic matter; it is on this account that fresh 

 cotton is with difficulty moistened with water, while it is at once decom- 

 posed if this coating of suberic matter is removed by the action of chlorine. 



Such at least is the opinion of Mitscherlich. It seems, however, that an 

 immersion in chlorine is not always sufficient to render this variety of cotton 

 capable of receiving color, the variety perfectly well known among dyers, 

 who have named it " dead cotton." It was first described by Daniel Koech- 

 lin, of Mulhouse, and has since been carefully studied by Walter Cram, of 

 Glasgow, whose results are published in the third volume of the Proceedings 

 of the Philosophical Society of Glasgoio. 



In the opinion of Mr. Walter Crum, the dyeing of cotton depends upon a 

 purely mechanical action. Chemistry is completely foreign to the subject of 

 fixing dyes upon stuffs. Dead cotton is the proof of this; the fibres of this 

 variety of cotton are flattened, while cotton which admits of being dyed is 

 composed of cylindrical fibres; the coloring matter, hence, can penetrate 

 within these, and fix itself there. 



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