THE TECHNOLOGIST. [Oct. 1, 1864. 



y» ON CHEMISTRY APPLIED TO THE ARTS. 



its solutions have a tendency to putrefy rapidly, but I have the pleasure 

 to inform you that a few drops of a substance called carbolic acid will 

 prevent putrefaction for a long period. Gelatine dissolves readily in 

 acetic acid, of moderate strength, or vinegar, and this solution, which is 

 used as glue, has the usetul property of remaining fluid and sound for 

 some time. But a Frenchman, named Demoulin, has introduced of late 

 years in Paris a solution of glue which is superior to the above and to 

 that in common use, because it does away with the trouble of constantly 

 heating the glue-pot. His process consists in melting one pound of 

 best glue in one pound of water, and adding gradually to the two one 

 ounce of nitric acid of sp. gr. 1-36, heating the whole for a short time, 

 when the fluid glue is prepared. The action of concentrated nitric acid 

 on gelatine is most violent, giving rise to several compounds, amongst 

 which may be cited oxalic acid. The action of sulphuric acid on gela- 

 tine is important in a scientific point of view, as an alkaloid called 

 leucine is produced, as well as a sweet substance, called glycocolle, or 

 sugar of gelatine. Gelatine is distinguished from other organic sub- 

 stances by the following chemical reactions : — it gives a white precipi- 

 tate with alcohol, also with chlorine, none with gallic acid, but one with 

 tannin, or tannic acid. The properties of this precipitate are most 

 important to us, as it is on the formation of it in hides that we ascribe 

 their conversion into leather. The relative proportion of these two 

 substances (gelatine and tannin) in the precipitate varies with the respec- 

 tive proportions brought in contact, but precipitates containing as much 

 as 46 per cent, of tannin have been examined. It is insoluble in water, 

 and presents the invaluable character of not entering into putrefaction. 

 Beautiful fancy ornaments have recently been introduced in Paris by 

 M. Pinson, called artificial tortoiseshell, which he obtains by melting, 

 at a moderate temperature, gelatine with a small amount of metallic 

 salts, running the whole into moulds, staining the mass with hydro- 

 sulphate of ammonia, so as to produce an imitation of the grain of 

 tortoiseshell. The objects so produced are then polished and ready for 

 sale. Before entering on the manufacture of various qualities of gela- 

 tine, I should wish to state that there can be do doubt, from the researches 

 of Magendie, as well as from the Report of the Commission appointed 

 by the Netherlands Academy of Sciences, that gelatine as food possesses 

 no nutritive value whatever. Allow me now to give you a rapid out- 

 line of the methods followed in the manufacture of various qualities of 

 gelatine. The first quality of gelatine is prepared by taking the clip- 

 pings, scrapings, and fleshings from the tanyard, treating them with 

 lime water or alkali, to remove any smell and certain impurities. They 

 are next washed and left in contact for a day or two with a solution of 

 sulphurous acid. They are then placed in a suitable apparatus, with 

 water, and heated, when the osseine is converted into gelatine. This is 

 run into a ^second vessel, and a little alum added, to throw down any 

 impurities that may be in suspension. The liquor is now ready to be 



