PARCHMENT, VEGETABLE 515 



that if a portion of vegetable parchment be heated over a flame, blisters will occur 

 from pent-up steam, -which are involved in the centre of the paper, and even in 

 the aerial state the vapour cannot pass either surface. The material of the meta- 

 morphosed surfaces is certainly one of the most unalterable and unchangeable of 

 all known organic substances, and requires a distinctive name to indicate its indi- 

 viduality. 



From Dr. Hofmann's report on this remarkable substance wo extract the following 

 remarks : 



' In accordance with your request, I have carefully examined the new material 

 called vegetable parchment, or parchment-paper, which you have submitted to me 

 for experiment; and I now beg to communicate to you the results at which I have 

 arrived. 



' I may here state that the article in question is by no means new to me. I became 

 acquainted with this remarkable production very soon after Mr.W. E. Gaino had made 

 known his results; and I have now specimens before me which came. into my posses- 

 sion as early as 1854. 



' The substance submitted to me for examination exhibits in most of its properties 

 so close an analogy with animal membrane, that the name adopted for the new 

 material seems fully justified. In its appearance, vegetable parchment greatly re- 

 sembles animal parchment : the same peculiar tint, the same degree of translucency, 

 the same transition from the fibrous to the horn-like condition. Vegetable, like 

 animal, parchment possesses a high degree of cohesion, bearing frequently-repeated 

 bending and rebending, without showing any tendency to break in the folds ; like the 

 latter it is highly hygroscopic, acquiring by the absorption of moisture increased 

 flexibility and toughness. Immersed in water, vegetable parchment exhibits all the 

 characters of animal membrane, becoming soft and slippery by the action of water, 

 without, however, losing in any way its strength. Water does not percolate through 

 vegetable parchment, although it slowly traverses this substance like animal mem- 

 brane by endosmotic action. 



' In converting unsized paper into vegetable parchment, or parchment-paper, by 

 the process recommended by Mr. Gaine viz. by immersion for a few seconds in oil of 

 vitriol diluted with half its volume of water I was struck by the observation how 

 narrow are the limits of dilution between which the experiment is attended with 

 success. By using an acid containing a trifle more of water than the proportion indi- 

 cated, the resulting parchment is exceedingly imperfect ; whilst too concentrated an 

 acid either dissolves or chars the paper. Time, also, and temperature are very impor- 

 tant elements in the successful execution of the process. If the acid-bath be only 

 slightly warmer than the common temperature, 60 Fahr. (15'5 Cent.) 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 be- 

 tween time, temperature, and concentration, appear to obtain with reference to this 

 process ; for an acid of inferior strength, when heated above the common tempera- 

 ture, 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 papers in any way similar to those which 

 you have submitted to me for experiment. 



' It is obvious that the transformation, under the influence of sulphuric acid, of 

 paper into vegetable parchment, is altogether different from the changes which vege- 

 table fibre suffers by the action of nitric acid ; the cellulose receiving, during its 

 transition into pyroxylin and gun-cotton, the elements of hyponitric acid in exchange 

 for hydrogen, whereby its weight is raised, in some cases by 40, in others by as 

 much as 60 per cent. As the nitro-cornpounds thus produced differ so essentially 

 in composition from the original cellulose, we are not surprised to find them also en- 

 dowed with properties altogether different ; such as increased combustibility, change 

 of electrical condition, altered deportment with solvents, &c., whilst vegetable parch- 

 ment, 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 additional value upon the original 

 substance. 



' The nature of the reaction which gives rise to the formation of vegetable parch- 

 ment having been satisfactorily established, it became a matter of importance 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 conversion into vegetable parch- 

 ment, can be permanently secured only by the entire absence or perfect neutrali- 



LL 2 



