628 



GEMS 



1084 



Fig. 1084 is an end view of tho apparatus ; a, the main steam -pipe ; a, 1>, c, c, branches 

 that conchict the steam to the bottom of tho cylinder ; o, the tackle for raising the 

 cage ; s, stopcock ; n, small glitter ; m, main conduit ; b, cistern of reception. 



When a strong and pure jelly is wished for, 

 the cylinder charged with the bones is to bo 

 wrapped in blanket-stuff; and whenever the 

 grease ceases to drop, the stopcock which admits 

 tho cold wa,ter is to be shut, as also that .-it tho 

 bottom of the cylinder, which is to be opened 

 only at the end of every hour, and so little as to 

 let the gelatinous solution run out, without allow- 

 ing any of tho steam to escape with it. 



Butchers' meat contains, on an average, in 100 

 pounds, 24 of dry flesh, 50 of water, and 20 of 

 bones. Those 20 pounds can furnish 6 pounds 

 of alimentary substance in a dry state ; whence 

 it appears that, by tho above means, one fourth 

 more nutritious matter can bo obtained than is 

 usually got. A keen dispute has been carried 

 on for some time in Paris, between the partisans 

 and adversaries of gelatine as an article of food. 

 It is probable that both parties have pushed 

 their arguments too far. Calf s-foot jelly is still 

 deemed a nutritious article by tho medical men 

 of this country, at least ; though it is not to bo 

 trusted to alone, but should have a due ad- 

 mixture or interchange of fibrine, albumen, 

 caseine, &c. See NUTRITION. 



French Gelatine is sold in cakes, marked, like 

 those of common glue, with the nets on which they have been dried. This gelatine 

 is made at Paris, from the cuttings of skins used for making white kid gloves; it is 

 coloured red, green, and blue, as well as sold colourless. 



Swinbourne's patent refined Isinglass is a pure form of gelatine, procured from tho 

 skins of calves cut into very thin slices and treated simply with water at or 

 about 200. 



D'Arcet, in his Eecherches sur Us Substances nutritives que rcnfermcnt les Os, states 

 that, in Paris, bones of all kinds are first digested with hydrochloric acid to extract 

 the phosphate of lime, and then boiled in water under pressure. In this way a 

 nutritious soup is prepared for the hospitals and other pauper establishments. 

 : Dr. T. Kichardson of Newcastle-on-Tyne treats bones first with muriatic or dilute 

 sulphuric acid to dissolve out a portion of the mineral phosphates which they 

 contain; the residue being then acted upon by sulphurous acid. The gelatinn 

 obtained after this process is treated with an alkaline sulphate or hyposulphato, or it 

 may be treated with the phosphates of an alkali, or with the sulphurous-acid solution 

 of the diphosphates of lime and magnesia. By any of these processes, it is said, the 

 hardness and sizing-propcrties of gelatine from any source may be very considerably 

 improved. See ISINGLASS. 



GEMS are precious stones, which, by their colour, limpidity, lustre, brilliant polish, 

 purity, and rarity, are sought after as objects of dress and decoration. Among these 

 beautiful minerals, mankind have agreed in forming a select class to which tho title 

 of gems or jewels has been appropriated ; while the term precious stone is more 

 particularly given to substances which occur of a larger size and more commonly. 



Diamonds, sapphires, emeralds, rubies, topazes, opals, hyacinths, and chrysoberyls, 

 are reckoned the most valuable gems. 



Crystalline quartz, pellucid, opalescent, or of various hues, amethyst, lapis-lazuli, 

 malachite, jasper, agato, &c., are ranked in the much more numerous and inferior class 

 of precious stones. These distinctions are not founded upon any strict philosophical 

 principle, but are regulated by a conventional agreement, not very well defined ; for it 

 is impossible to subject these creatures of fashion and taste to tho rigid subdivisions of 

 science. "We have only to consider tho value currently attached to them, and take caro 

 not to confound two stones of tho samo colour, but which may be very differently prized 

 by the virtuoso. 



Since it usually happens that the true gems are in a cut and polished state, or oven 

 pot in gold or silver, wo are thereby unable to apply to them many of the criteria of 

 mineralogical and chemical science, Tho cutting of tho stone has removed or ni.-isked 

 its crystalline character, and the phenomena of double or single refraction are often 

 difficult to be observed; whilst tno test by the blowpipe is inadmissible. Hence tho 



