CHEMISTRY. 



145 



tion of 

 Nature. 



rliemical ed to remain at rest for some hours, to give the remain- 

 Examina- (j er o f t ( !e cur d time to precipitate is decanted off almost 

 as colourless as water, and scarcely any of the peculiar 

 taste of milk can be distinguished in ir. If it be now 

 slowly evaporated, it deposites at hst a number of white- 

 coloured crystals, which are sugar of milk. Toward the 

 end of the evaporation, some crystals of muriate of pot- 

 ash and of muriat'j of soda make their appearance. Ac- 

 cording to Scheele, it contains also a little phosphate of 

 lime, which may be precipitated by ammonia. 



The recent experiments of Fourcroy and Vauquelin, 

 Thenard, and Bouillon La Grange, have added consi- 

 derably to our knowledge of the constituents of whey. 

 It always reddens vegetable blues, containing a portion 

 of acetic acid. The lactic acid of Scheele is nothing 

 else than this acid holding an animal matter in solution. 

 It contains likewise some phosphate of magnesia and 

 phosphate of iron, as Fourcroy and Vauquelin have dis- 

 covered. Sulphate of potash, likewise, and a peculiar 

 extractive matter, have been separated from it. 



Thus we see that cow's milk is composed of the fol- 

 lowing ingredients : 



Composi - 

 tion <>f 

 cow't milk. 



1. Water. 



2. Oil. 



3. Curd. 



4. Extractive. 



5. Sugar of milk. 



6. Acetic acid. 



7. Muriate of soda. 



8. Muriate of potash. 



9. Sulphate of potash. 



10. Phosphate of lime. 



11. Phosphate of magnesia. 



12. Phosphate of iron. 



The milk of all other animal*, as far as it has hitherto 

 been examined, consists nearly of the same ingredients ; 

 but there is a very great difference in their proportion. 



SECT. XI. Of Saliva. 



Saliva. The fluid secreted in the month, which flows in con- 



siderable quantity during a repast, is known by the name 

 of tuliea. 



Its pro- Saliva is a limpid fluid like water, but much more 



pcrtiej. viscid. It has neithrr smell nur taste. Its specific gra- 

 vity, according to Himbrr^er, is 1.0167 ; according to 

 Siebc'ld, 1.0X0. When agitated, it froths like all other 

 adhesive liquids ; indeed it is usually mixed with air, and 

 has thv appearance of froth. 



It m it her mixes readily with water nor oil ; but by 

 tritur.tion in a mortar, it maybe so mixed .vith w; ( r as 

 to pass through a filter. It h^ a -rreat sffinif for oxy- 

 gen, ab.'orbs it rradily from the air, and gives it out again 

 to otli.-r bodies. 



When boiled in water, a few flak'-s r,f albumen preci- 

 pi'.ate. From the experiments of Dr B>. stock, we learn 

 that this albumen is not in a state of solmiun. It i -e- 

 p.-. rated by t'i- filfr. and subside* of it< own accord 

 when th. liquid is di!utrd .vith water. In his analysis, 

 thK coagulated alburrun amounted to 0.4> of the solid 

 matt- r contained in the saliva ex imined. 



W.'ien saliva is evaporated, it swt-lls exceedingly, and 

 leaves behind it a 'hm brown coloured crust ; but if the 

 evaporation be conducted slowly, small cubic crystals of 

 muriate ot soda are formed. The vscrdity of salivi, the 

 property which it has of absorbing oxygen, and of be- 

 inspisaated, announce rhe presence of mucus as a 

 r.wnf part. This is fully confirmed by the effect 

 of neulr<ti ac.-late of It ad, which produces a copious pre- 

 cijiit , i. Dr Bostock coi. -iders the mu. 



constituting about one-half of the solid contents of sa- 

 liy.i. 



W.i n s liva is distilled in a retort, it froth wry much ; 

 100 p 80 parts .if writer < 



tie carho:. i.nouia, some oil, and an acid, which 



VOL. VI. PART I. 



Nature. 



Composi- 

 tion. 



perhaps is the prussic. The residuum amounts to about Chemical 



1.56 part, and is composed of muriate of soda, phosphate Examina- 



r j i_ L . r i- lion ot 

 of soda, and phosphate or lime. 



The acids and alcohol inspissate saliva ; the alkalies 

 disengage ammonia ; oxalic acid precipitates lime ; and 

 the nitrates of lea'd, mercury, and silver, precipitate phos- 

 phoric and muriatic acids. 



From these facts, it follows that saliva, besides water, 

 which constitute* at least four fifths of its bulk, contains 

 the following ingredients: 



1. Mucilage. 4. Phosphate of soda. 



2. Albumen. 5. Phosphate of lime. 



3. Muriate of soda. 6. Phosphate of ammonia. 

 But it cannot be doubted, that, like all the other animal 

 fluids, it is liable to many changes from disease, &c. 

 Brugnatelli found the saliva of a patient labouring under 

 an obstinate venereal disease impregnated with oxalic 

 acid. 



SECT. XII. Of Bile. 



Bile is a liquid of a yellowish green colour, an unctu- Bile, 

 ous feel, bitter taste, and peculiar smell, which is secre- 

 ted by the liver j and, in most animals, considerable 

 quantities of it are usually found collected in the gall 

 bladder. 



1. Ox bile is a liquid of a yellowish green, and some- Ox bile, 

 times of a deep green colour. Its taste is very bitter, 

 but at th>' same time sweetish. Its smell is feeble, but 

 peculiar and disagreeable. It does not act on vegetable 

 blues. Its consistence varies very much. Sometimes it 

 is a thin nincil :ge ; sometimes very viscid and glutinous ; 

 sometimes it is perfectly transparent ; and sometimes it 

 contains a yellow-coloured matter, which precipitates 

 when the bile is diluted with water. 



When an acid is added to bile, even in a minute quan- 

 tity, it acquires llv prop- rty ot reddening vegetable 

 blues. The addition of a little more acid occasions 

 a precipitate, and t>ulphuric acid occasions a greater 

 precipitate than any other acid. This precipitate con- 

 sists of a yellow-i-ol.jured matter often visible in bile, 

 and which is insoluble in water. It contains also a little 

 resin, which gives it a bitter taste. Acids do not throw 

 down the whole resin from bile. Yet if the resin be dis- 

 m soda, it is readily precipitated by all the acids ; a 

 proof thdt the resin is not kept in solution in bile by soda. 

 When superacetate of lead is poured into bilr, a co- 

 pious white precipitate fjlls, consisting of the resin com- 

 bined with the .ixide of lead. The superacetate of com- 

 merce does not readily throw down the whole resin ; 

 but if eight parts of common sugar of lead and one part 

 of litharge be unked together by digestion in w.-tt-r, a 

 sjlt is formed, wii.c.i re.idily throw^i down the 

 the resin, if the precipitate be treated wi.h dilut.-J ni- 

 tric acid, the lead is separated, and the resin r-mains be- 

 hind in a stale of purity. It is a green coloured bitter 

 tasted sub.tance, possessing most of tiie pr,/pi.rties of 

 resins. It has been already described in the pn ceding 

 Section. One hundred parts of bile contain about u,ree 

 parts nf re;'n. 



If acetate of lead be poured into bile thus deprived of 

 i i by the superacetate, a new a'.id mor- copious 

 pncipitate falls, consisting of the oxide of iirfd united to 

 1 ar substance, wh:ch gives bile most of its charac- 

 ter*. This substance was first described in detail by 

 Thcuard, who has given it the name of picromrt. The 

 co-r pound, consisting of oxide of lead and picromcl, is 

 PI .icetic acid. If a current of sulpiuim .1 hy- 

 drogen gas be passed through the solution, the lead is 



