324 ANNUAL OF SCIENTIFIC DISCOVERY. 



the written or traced surface ; by either of which acts the salts will receive 

 the necessary supply of moisture to enable them to form double decompo- 

 sition, and produce chemical marks or writing on the paper. The salt or 

 salts preferred for making dry salt chemical pencil, for producing chemical 

 writing or marking, of the character described, are the tartrate of iron, the 

 hypersulphate of iron, or any of the permanent iron salts. 



Heretofore it has been a desideratum to obtain a superior substitute for 

 the common lead or plumbago pencil and the crayon, and also for the 

 method of writing with a fluid-like ink. The lead pencil and crayon only 

 make mechanical marks, which are easily erased ; and writing with ink is 

 troublesome, because the pen has to be often replenished. 



This improved method or process will produce chemical marks or writ- 

 ing equal to those made by inks ; and the method of writing or producing 

 them is as easy as the act of writing with a common pencil. It will be a 

 superior method of writing on books and bills, and making permanent re- 

 cords on paper. It will afford security against alteration of the writing on 

 records, as it will require the specific salts in the pencil and paper to pro- 

 duce a writing similar in color and shade to that which is attempted to be 

 supplanted, changed, or altered, and to that on the part of the document 

 written upon. This process obviates the evils and objections incident to the 

 use of a common pencil or pen and ink. 



The patentee claims " producing chemical marks, records, or writing, on 

 chemically prepared paper, as described, by tracing, pressing, or writing 

 with a chemically prepared pencil, style, tracer, type, or other suitable in- 

 strument, on such paper, under the hygroscopic conditions herein described, 

 or in any manner substantially the same." 



PARCHMENT PAPEK. 



At a recent meeting of the Royal Institution, Mr. J. Barlow, F. R. S., 

 presented the following communication, on the new product, known as 

 "Parchment Paper/' recently invented by Mr. W. E. Gaine. 



The compounds of woody-fibre are carbon, hydrogen, and oxygen; the last- 

 named elements being combind in the same proportion as they exist in water. 

 In this respect woody-fibre is identical with starch, dextrine, gum, and 

 susrar. Unlike these substances, it is insoluble whether in water, ether, 

 alcohol, or oil, and much more averse than they arc to chemical change. 

 Mr. Barlow called attention to the enormous inconvenience which would 

 arise if water could dissolve cloth, or if vegetable tissues Avere easily de- 

 composed. It is, however, many years since Braconnot discovered that 

 sawdust, linen, and cotton fabrics, &c., could be made to part with a 

 portion of their constituent hydrogen in exchange for an oxide of nitro- 

 gen obtained from the decomposition of the nitric acid Avith Avhich they 

 Avere treated. Pelouze aftcnvards applied this principle in operation on 

 paper ; and to the same principle must be ascribed the gun-cotton and 

 collodion of Schonbein. Taking Avhat may be called the gun-paper (Pcl- 

 ouze's paper) as a type of all these substances, Mr. Barlow showed by 

 experiment that it is inflammable and highly electrical, and that in con- 



