CHEMISTRY. 



' ...tr.l-ll 

 I 1 . . 13- 



Nature. 



Urea. 



HowoU- 



::iproptr 

 tic*. 



great diversity of these substances ii well known. The 

 muscle* of fish, of fowl, and of quadrupeds, bear scarcely 

 any rrtcmblance to each other. 



SECT.V. Ofl'rra. 



Urea may be obtained by the following process : Eva. 

 porate by a gentle heat a quantity of lr.iir.an urine, void- 

 ed MX or eight hours after a rne.il, till it be reduced to 

 the consistence of a thick syrup. In this state, when 

 put by to cool, it concrete! into * cryitelline mas. 

 Pour at different t;m upon this mass four time* it 

 weight of alcohol, and apply a gentle heat ; a great part 

 of the mass will be dissolved, and there will remain only 

 a number of saline substances. Pour the alcohol solu- 

 tion into a retort, and distil by the heat of a sand bath, 

 till the liquid, after boiling some time, is reduced to the 

 consistence of a thick syrup. The whole of the alcohol 

 is now separated, and what remains in the retort crystal- 

 lizes as it cools. These crystals consist of the substance 

 known by the name of urea. 



Urea, obtained in this manner, has the form of crystal- 

 line plates crossing each other in different directions. Its 

 colour is yellowish- white : it has a fetid smell, somewhat 

 resembling that of garlic or arsenic ; its taste is strong 

 and acrid, resembling that of ammomacal salts j it is very 

 viscid and difficult to cut, and has a good deal of resem- 

 blance to honey. When exposed to the open air, it very 

 soon attracts moisture, and is converted into a thick 

 brown liquid. It is extremely soluble in water ; and 

 during its solution a considerable degree of cold is pro- 

 duced. Alcohol dissolves it with facility, but scarcely 

 in so large a proportion as water. The alcohol solution 

 yields crystals much more readily on evaporation than the 

 solution in water. 



When nitric acid is dropt into a concentrated solution 

 of urea in water, a great number of bright pearl-colour- 

 ed crystals are deposited, composed of urea and nitric 

 acid. No other acid produces this singular effect. The 

 concentrated solution of urea in water is brown, but it 

 becomes yellow when diluted with a large quantity of 

 water. The infusion of nutgalls gives it a yellowish- 

 brown colour, but causes no precipitate ; neither does 

 the infusion of tan produce any precipitate. 



When heat is applied to urea, it very soon melts, swells 

 :;p, anil evaporates with an msupportably fetid odour. 

 When distilled, there comes over first bcnzoic acid, then 

 carbonate of ammonia in crystals, some carbureted hy- 

 drogen gas, with traces of prussic acid and oil; and 

 there remains behind a large residuum, composed of 

 charcoal, muriate of ammonia, and muriate of soda. The 

 Distillation is accompanied with an almost insupportably 

 fetid alliaceous odour. 



When the solution of urea in water is kept in a boil- 

 ing heat, and new water is added as it evaporates, the 

 ;rca is gradually decomposed, a very great quantity of 

 carbonate of ammonia is disengaged, and at the same 

 time acetic acid is formed, and some charcoal precipi- 

 tates. 



When a solution of urea in water is left to itself for 

 same time, it it gradually decomposed. A froth col- 

 lects on its surface ; air bubbles are emitted, which have 

 a strong disagreeable smell, in which ammonia and ace- 

 tic acid are distinguishable. The liquid contains a quan- 

 tity of acetic acid. The decomposition is much more 

 rapid if a little gelatine be added to the solution. In that 

 case more ammonia is disengaged, and the proportion of 

 acid is not so great. 



When the solution of urea is mixed with one-fourth -of 



its weight of diluted sulphuric acid, no effervescence tal 

 place; but, on the application of heat, a quantity of oil 



I i 1 



appears on the urtcr, winch concretes upon cooling ; N.nurc. 

 the liquid which comes over into the i tains > -_ ^^ 



acetic acid, and a quantity of sulphate of ammonia re- 

 mains in the retort dissolved in the undiktilled mass. By 

 repeated distillations, the whole of ihe urea is converted 

 into acetic acid and ammonia. 



When nitric acid is poured upon crystallized urea, a 

 violent effervescence takes place, (he mixture frothes, as- 

 sumes the form of a dark red liquid, gnat quantitirs of 

 nitrous gas, azotic gas, and carbonic acid ga, arc dr 

 gaged. When the effervescence is over, there remains 

 only a concrete white matter, with some drops of red- 

 dish liquid. When heat is applied to this residuum, it 

 detonates like nitrate of ammonia. 



Muriatic acid dissolves urea, but docs not alter ir. 

 Oxymuriatic acid gas is absorbed very rapidly by a dilu- 

 ted solution of urea ; small whitish flakes appear, which 

 soon become brown, and adhere to the sides of the ves- 

 sel like a concrete oil. After a considvrable quantity of 

 oxymuriatic acid had been absorbed, the solution, left to 

 itself, continued to effervesce exceeding tlowly, and to 

 emit carbonic acid and azotic gas. Alter this <.;!. rvcs- 

 cence was over, the liquid contained muriate and carbon- 

 ate of ammonia. 



Urea is dissolved very rapidly by a solution of potash 

 or soda, and at the same time a quantity of ammonia is 

 disengaged j the same substance is disengaged when urea 

 is treated with barytes, lime, or even magnesia. Hence 

 it is evident, that this appearance must be ascribed to 

 the muriate of ammonia, with which it is constantly 

 mixed. When pure solid potash is triturated with urea, 

 heat is produced, a great quantity of .ammonia is disen- 

 gaged ; the mixture becomes brown, and a substance is 

 deposited, having the appearance of an empyreumatic oil. 

 One part of urea and two oi potash, dissolved in four 

 times its weight of water, when distilled, give out a 

 great quantity of ammoniacal water ; the residuum con- 

 tains acetate and carbonate of potash. 



When mviriate of soda is dissolved in a solution of 

 urea in water, it is obtained by evaporation, not in cubii: 

 crystals, its usual form, but in rectangular octahed- 

 Muriate of ammonia, on the contrary, which crystallizes 

 naturally in octahedrons, is converted into cubes, by di<- 

 solving and crystallizing it in the solution of urea. 



SECT. VI. Of Saccharine Mailer. 



Sugar has never been found in animals in every respect saccharine 

 similar to the sugar of vegetables j but there are certain matter in 

 animal substances which have so many properties in com- aiiimxl srl.- 

 mon with sugar, that they can scarcely be arranged un- "' 

 der any other name. These substances nre, 

 1. Sugar of milk. 

 '2. Honey. 

 3. Sugar of diabetic urine. 



1 . Sugar of milk may be obtained by the following Sujj;lr , 

 process : Let fresh whey be evaporated to the consist- m ilk. 

 cnce of honey, and then allowed to cool ; it concretes 

 into a solid mass. Dissolve this mass in water, clarity it 

 with the white of eggs, filter and evaporate to the con- 

 sistence of a syrup,; it depusites, on cooling, a number 

 of brilliant white cubic crystals, which arc sugar of milk. 



When pure, it has a white colour, a sweetish taste, and 

 no smell. Its crystals are semitrantiparent regular paral- 

 lelopipeds, terminated by four-oided pyramids. Its spe- 

 cific gravity, at the temperature of 55, is 1.543. At 

 that temperature it ie soluble in seven times its weight 



