Oct. 1, 1864.] THE TECHNOLOGIST. 



ON CHEMISTRY APPLIED TO THE ARTS. 101 



interesting class of substances, these curious gelatinous products, which are 

 not only considered great delicacies in China and other parts of the East, 

 but even in Europe,where they realize from 31. to 11. per pound ; some are 

 occasionally imported into England. It has long been a disputed question 

 what is the chemical nature of the substance composing these nests, which 

 ar« the product of a peculiar kind of swallow ; but Mr. Payen, by his 

 recent researches, has left no doubt in the minds of chemists that it is 

 an animal, not a vegetable matter. In fact, it is a peculiar mucous 

 substance, secreted by the bird, and composed of carbon, hydrogen, 

 oxygen, nitrogen, and sulphur. Further, it is insoluble in cold water, 

 but soluble in boiling, and differs from gelatine and isinglass in that it 

 does not gelatinize as it cools. 



Skins. — Skin consists of two principal parts, one a mere film, called 

 the epidermis, and the other constituting the bulk of the skin, and 

 called the dermis. There are, also, found in skin a large quantity of 

 blood-vessels, and a small quantity of pigment cells, which hold colour- 

 ing matter. Further, the skin contains a small amount of nerves and a 

 number of glands, among which may be cited the sebaceous glands or 

 follicles, which are intended to secrete the unctuous matter constantly 

 accumulating upon the skin, and keeping it soft and pliable ; then there 

 are perspiratory glands, which play a most important part in the physiolo- 

 gical construction of the skin. These are so numerous that Mr. Erasmus 

 Wilson has calculated that there are 3,528 of them in a single square 

 inch of human skin, so that in an ordinary-sized body there are no less 

 than 2,300,000 of these pores. But still the most important part of the 

 hide for us is that called the " dermis." The skins of animals are com- 

 mercially divided into three distinct classes. The hide is the name 

 given to the skin of full-grown animals, such as oxen, horses, and 

 buffaloes ; and these are further sub-divided into fresh hides, that is to 

 say, those which are obtained from animals slaughtered in this country ; 

 dry hides, that is hides which have been stretched in the sun, and which 

 are principally imported from South America ; dry salted hides, princi- 

 pally from the Brazils, where they are salted and then dried in the sun ; 

 and salted hides, which are preserved at Monte Video and Buenos Ayrea 

 by salting them, and are then shipped, imbedded in salt, to this country. 

 The composition of a fresh hide may be considered to be as follows : — 



Kealskin 32-53 



Albumen T54 



Animal matters soluble in alcohol . 0-83 



Animal matters soluble in cold water . 7*60 



Water 57'50 



100-00 



A second class of hides is that called kips, which are skius flayed from 

 the same kinds of animal as the foregoing, only when young. Thirdly, 



