CHEMICAL SCIENCE. 249 



than the common temperature, 00 F. (15'5 C.) such as may happen when 

 the mixture of acid and water has not been allowed sufficiently to cool the 

 effect is very considerably modified. Nor do the relations usually observed 

 between time, temperature, and concentration, appear to obtain with refer- 

 ence to this process; for an acid of inferior strength, Avhen heated above the 

 common temperature, or allowed to act for a longer time, entirely fails to 

 produce the desired result. Altogether the transformation of ordinary paper 

 into vegetable parchment is an operation of considerable delicacy, requiring 

 a great deal of practice; in fact, it was not until repeated failures had pointed 

 out to me the several conditions involved in this reaction, that I succeeded in 

 producing the substance in question. 



Mr. Barlow, in the discourse on woody fibre, records some experiments es- 

 tablishing that unsized paper, by its conversion into vegetable parchment, 

 receives no appreciable increase of weight. These experiments rendered it 

 very probable that the action of sulphuric acid in this case is essentially 

 molecular, and that the chemical composition of the substance of the paper, 

 by its conversion into parchment, is not altered. It remained to establish this 

 point experimentally. For this purpose several of the specimens of com- 

 mercial vegetable parchment, without any further purification, were submit- 

 ted to analysis. The result showed that with the exception of about 09 

 per cent, of mineral matter, a quantity, not much exceeding the amount 

 which is present in the better varieties of ordinary paper the substance of 

 vegetable parchment is identical in composition with cellulose or woody 

 fibre. The analytical experiment demonstrates as might have been ex- 

 pected that the extraordinary change which the properties of paper undergo 

 during its transformation, depends solely and exclusively upon a molecular 

 rearrangement of the constituents, and not upon any alteration in the com- 

 position of the paper. In this respect the action which sulphuric acid exerts 

 upon woody fibre may be compared to the transformation of woody fibre, 

 under the protracted influence of the same agent, into dextrin, a substance 

 altogether different from fibre, but still identical with it in composition. 

 Vegetable parchment may, in fact, be looked upon as the connecting link 

 between cellulose on the one' hand, and dextrin on the other. 



Thus it is obvious that the transformation, under the influence of sulphuric 

 acid, of paper into vegetable parchment, is altogether different from the 

 changes which vegetable fibre suffers by the action of nitric acid; the cellu- 

 lose receiving, during its transition into pyroxylin and gun-cotton, the ele- 

 ments of hyponitric acid in exchange for hydrogen, whereby its weight is 

 raised, in some cases by forty, in others by as much as sixty per cent. As 

 the nitro-compounds thus produced differ so essentially in composition from 

 the original cellulose, we are not surprised to find them also endowed with 

 properties altogether different, such as increased combustibility, change of 

 electrical condition, altered deportment with solvents, etc.; whilst vegetable 

 parchment, being the result of a molecular transposition only, in which the 

 paper has lost nothing and gained nothing, retains all the leading characters 

 of vegetable fibre, exhibiting only certain modifications which confer addi- 

 tional value upon the original substance. 



The nature of the reaction which gives rise to the formation of vegetable 

 parchment having been satisfactoi'ily established, it became a matter of im- 

 portance to ascertain whether the processes used for the mechanical removal 

 of sulphuric acid from the paper had been sufficient to produce the desired 

 effect. It is obvious that the valuable properties acquired by paper, by its 



