250 ANNUAL OP SCIENTIFIC DISCOVERY. 



conversion into vegetable parchment, can be permanently secured only by 

 the entire absence or perfect neutralization of the agent which produced 

 them. The presence of even traces of free sulphuric acid in the paper would 

 rapidly loosen its texture, the paper would gradually fall to pieces, and one 

 of the most important applications which suggest themselves, viz., the use 

 of vegetable parchment in the place of animal parchment for legal docu- 

 ments, would thus at once be lost. 



Examination of the vegetable parchment for the free sulphuric acid, was 

 therefore one of the principal points to which I had to direct my attention. 

 From the description of the process adopted in preparing the new material, 

 viz., long-continued mechanical washing with cold water, immersion in a 

 dilute solution of caustic ammonia, and, lastly, renewed washing with water, 

 the absence in it of free sulphuric acid may be at once inferred on scientific 

 grounds. For, supposing that the first process of washing had left any free 

 sulphuric acid in the paper, this acid, after immersion of the paper in caustic 

 ammonia, for which it has so strong an attraction, could have remained only 

 in the form of sulphate of ammonia, a salt of perfectly neutral composition, 

 in which the acid character of sulphuric acid is entirely lost. Now, sulphate 

 of ammonia is a most stable compound, which begins to decompose only at 

 about 530 F. (280 C.), a temperature at which paper is completely destroyed; 

 and even then, no free sulphuric acid is to be found amongst the products of 

 decomposition. But the paper is washed again after treatment with ammo- 

 nia, and, obviously, only traces of sulphate of ammonia can remain in it. 



The absence of free sulphuric acid in the parchment paper was, moreover, 

 established by direct experiment. The most delicate test-papers, left for 

 hours in contact with moistened vegetable parchment, did not exhibit the 

 slightest change of color. There is reason, therefore, to believe that vegeta- 

 ble parchment, prepared as it is by one of the most powerful agents of 

 decomposition, carries within itself the germ of its own destruction. 



The absence of free sulphuric acid in vegetable parchment having been 

 satisfactorily established, it remained only to perform a few experiments on 

 the strengh of this material as compared with that of the animal parchment, 

 with which it is likely to enter into competition. The result of these led to 

 the result that paper, by exposure to the action of sulphuric acid in the man- 

 ner described, acquires about five times the strength which it previously pos- 

 sessed, and that for equal weights, vegetable parchment possesses about 

 three-fourths the strength of animal parchment. It was found, moreover, 

 that bands of vegetable parchment taken from different sheets of the same 

 kind of paper, exhibited a remarkable uniformity of strength, whilst in ani- 

 mal parchment which, owing to its mode of manufacture, must always 

 present considerable inequality of thickness extraordinary variations were 

 observed, even if the bands were taken from the same skin. 



Vegetable parchment, then, as far as strength goes, is not quite equal to 

 animal parchment. On the other hand, the new article greatly surpasses 

 real parchment in its resistance to the action of chemical agents, and espe- 

 cially of water. As has been already stated, vegetable, like animal parch- 

 ment, absorbs water, and becomes perfectly soft and pliable; but it may re- 

 main in contact, and even may be boiled with water for days, without being 

 affected in the slightest degree, retaining its strength, and regaining its origi- 

 nal appearance on drying; on the other hand, it is well known how rapidly 

 animal parchment is altered by boiling water, by the protracted action. of 

 which it is converted into gelatine. Even at the common temperature, ani- 



