CHEMISTRY. 



ivH 



Chemical 



Uiamiua- 



tton of 



Nuure. 



Dry gelatine undergoes no change when kept; but in 

 the gelatinous state, or when dissolved in water, it very 

 soon putrefies ; an acid makes its appearance in the first 

 place, (probably- the acetic.) a fetid odour is exhaled, 

 and afterwards ammonia is formed. 



Acids dissolve gelatine with facility, even when dilu- 

 ted, especially when assisted by heat ; but we are still 

 ignorantof the changes produced upon it by these agents, 

 except by nitric acid. When this acid is digested on it, 

 a small quantity of azntic gas is disengaged, then abun- 

 dance of nitrous gas ; the gelatme is dissolved, except 

 an oily matter which appears on the surface, and con- 

 verted partly into oxalic and malic acids. 



Alkalies dissolve gelatine with facility, especially when 

 assisted by heat ; but the solution does not possess the 

 properties of soap. 



None of the earths seem to combine with gelatine ; at 

 Last they do not precipitate it from its solution in wa- 

 ter. 



The metals, in their pure state, have no effect upon 

 gelatine ; but several of the metallic oxides, when agita- 

 ted in a solution of gelatine, have the property of depri- 

 ving the water of the greatest part of that body, with 

 winch they form an insoluble compound. Several of 

 the metallic salts likewise precipitate gelatine from wa- 

 ter. 



Gelatine is insoluble in alcohol. When alcohol is mix- 

 ed with a solution of gelatine, the mixture becomes 

 milky ; but becomes again transparent when agitated, 

 unless the solution be concentrated, and the quantity of 

 alcohol considerable. Gelatine is most probably equally 

 insoluble in ether ; though I believe the experiment has 

 not been tried. 



When the solution of tannin is dropt into gelatine, a 

 copious white precipitate appears, which soon forms an 

 elastic adhesive mass not unlike vegetable gluten. This 

 precipitate is composed of gelatine and tannin ; it soon 

 dries in the open air, and forms a brittle ivsmou -like 

 substance, insoluble in water, capable of resitting the 

 greater number of chemical agents, and not susceptible 

 of putrefaction. 



Gelatine dots not, properly speaking, combine with 

 oils, but it renders them miccible with water, and forms 

 a kind of emulsion. 



From the effects of different re-agents on gelatine, and 

 from the decomposition which it undergoes when heated, 

 we see that it contains carbon, hydrogen, azote, and 

 oxygen. The phosphate of lime, and the traces of so- 

 da, which it always yields, are most likely only held in 

 solution by it. The constituents, according to the ex- 

 periments of Thenard and Gay-Lussac, was as follows: 

 Carbon, 67>.s 1 

 Oxygen, 27-207 

 Hydrogen, 7.9 It 

 Azote, 16.998 



100 



SECT. II. Of Albumen. 



Albumen. The eggs of fowls contain two very different sub- 

 stances : a yellow oily-like matter, called the yolk; 

 and a colourless glossy viscid liquid, distinguished by 

 the name of while. This last is the substance which 

 chemists have agreed to denominate albumen. The white 

 of an egg, however, is not pure albumen. It contains 

 also tome mucus, soda, and sulphur : but as albumen is 

 never found perfectly pure, and as no method is known 

 of separating it, without at the same time altering the 



properties of the albumen, chemists arc obliged to cxa- Citemica* 

 mine it while in combination with these bodies. 



Albumen dissolves readily in water, and the solution ^. 10 ' 



ii_ c ' ' i 11 iNatuic* 



has the property or giving a green colour to vegetable ^_- _.-' 

 blues, in consequence of the soda which it contains. Its propci - 

 When albumen is heated to the temperature of 165, it ties. 

 coagiiLttes into a white solid mass ; the consistency of 

 which, when other things are equal, depends, in some 

 measure, on the time during which the heat was ap- 

 plied. The coagulated mass has precisely the same 

 weight that it had while fluid. This property of coa- 

 gulating when heated is characteristic of albumen, and 

 distinguishes it from other bodies. 



The taste of coagulated albumen is quite different, 

 from that of liquid albumen : its appearance, too, and 

 its properties, are entirely changed; for it is no longer 

 soluble, as before, either in hot or in cold water. 



The coagulation of albumen takes place even though 

 air be completely excluded ; and even when air is pre- 

 sent, there is no absorption of it, nor does albumen in 

 coagulating change its volume. Acids have the pro- 

 perty of coagulating albumen, as Scheele ascertained. 

 Alcohol also produces, in some measure, the same ef- 

 fect. Heat, then, acids and alcohol, are the agents 

 which may be employed to coagulate albumen. 



It is remarkable, that if albumen be diluted with a 

 sufficient quantity of water, it can no longer be coagu- 

 lated by any of these agents. 



We see, therefore, that albumen ceases to coagulate 

 whenever its particles arc separated from each other be- 

 yond a certain distance. That no other change is pro- 

 duced, appears evident from this circumstance, that 

 whenever the watery solution of albumen is sufficiently 

 concentrated by evaporation, coagulation takes place, 

 upon the application of the proper agents, precisely as 

 formerly. 



It does not appear that the distance of the particles of 

 albumen is changed by coagulation ; for coagulated al- 

 bumen occupies precisely the same sensible space as li- 

 quid albumen. 



Albumen, then, is capable of existing in two states ; 

 the one before it has been coagulated, and the other af- 

 ter it has undergone coagulation. Its properties are ve- 

 ry different in each. It will be proper therefore to con- 

 sider them separately. 



Albumen, in its natural state, or uncoagulatcd, is a 

 glary liquid, having little taste and no smell. When 

 dried spontaneously, or in a low heat, it becomes a brittle . 

 transparent glassy-like substance ; which, when spread 

 thin upon surfaces, forms a varnish, and is accordingly 

 employed by bookbinders for that purpose. When thus 

 dried, it has a considerable resemblance to gum arabic, 

 to which also its taste is similar. The white of an egg 

 loses about four-fifths of its weight in drying. It is stifl 

 soluble in water, and forms the same glary liquid as be- 

 fore. 



From the experiments of Dr Bostock, it appears, that 

 when one part of this dry albumen is dissolved,, in nine 

 parts of water, the solu'ion becomes perfectly solid when 

 coagulated by heat ; but if the albumen amounts only to 

 T', th of the liquid, then, though coagulation takes place, 

 the liquid docs not become perfectly solid, but may be 

 poured from one vessel to another. 



When one grain of albumen is dissolved in 1000 grains 

 of water, the solution becomes cloudy when heated. 



I. Uncoagulated albumen soon putrefies, unless it be Uncoagula- 

 dried; in which state it does not undergo any change, ted albu- 

 It putrefies more readily when dissolved in a large quan- men. 

 tity of water, than when concentrated. The smtll of the 



