ALA

ALB

t

( 23 )

From the concurrence of tins analysis withthat of Vauquelin, it may be concluded thatthe above are the ingredients which enter intothe compostion of the alum-stone of La Tolfa.The difference in the respective proportionsobtained by these able chemists depends in part,no doubt, on a want of perfect uniformity indifferent portions of the mineral itself.

ALBUMEN.

Dr. Bostock has given some useful obser-vations concerning this substance. 1 Whenwhite of egg is coagulated by heat and thenlong digested in water, about a fourth part is dis-solved, the remainder being untouched. Whiteof egg also loses about 80 per cent, of itsweight by gentle drying, -which loss appears tobe pure water. When water containing onlya thousandth part of pure albumen is heated toboiling its presence is indicated by a perceptibleopacity. The pure albumen here mentionedis reckoned to constitute 15j per cent, of theentire white of egg. A solution of albumen ofthe above strength is rendered milky by a fewdrops of corrosive sublimate solution, and aftera while a curdy precipitate collects. Nitro-muriat of tin has a similar effect but is notquite so powerful. Equal parts of an infusionof galls (half an ounce to half a pint of water)and a solution of rffoo of pure albumen form aprecipitate after standing a time. Goulard’sextract (a saturated solution of litharge in hotvinegar) precipitates albumen very speedily.

Most of these and other substances whichcoagulate albumen also act upon other animalfluids, but Dr. B. considers the coagulation byheat alone and by corrosive sublimate as ex-clusively belonging to albumen when comparedwith jelly and mucus. When corrosive subli-mate is first added to a solution of albumenand heat afterwards applied, the coagulation isvery complete, and the coagulum separable froma very dilute solution, but then it is a solidcompound of albumen with oxyd of mercury.The solution of tan, though considered as theappropriate precipitant of jelly, will also affecta solution of albumen, though not to the samedegree, and the compound precipitate of tan andthe animal matter is not so dense and separablefrom the liquid when albumen is present.

Almost every metallic solution is precipitatedby albumen, b and this precipitate then consistsof acid, metallic oxyd and albumen, but it isagain soluble more or less completely in anexcess of albumen. Hence it may be inferred

that it is the albumen which holds ill solutiottthe oxyd of iron met with in the blood.

Mr. Brande has given some very valuablefacts respecting the detection of small quantitiesof albumen by the galvanic action. c Whenthe conductors from a galvanic battery arebrought near each other in white of egg, animmediate and rapid coagulation takes place atthe negative wire but only a thin film of albu-men forms at the positive wire. This has beenexplained on an idea first suggested by Dr.Thompson, namely that the fluidity of albumendepends on the presence of alkaline matter,the separation of which at the negative polecauses the albumen to assume a solid form.

Pursuing this idea, Mr. Brande coagulatedsome white of egg by heat and then extractedby hot water that portion of the coagulumwhich (as observed by Dr. Bostock) is againsoluble in water, this solution was then exposedto the galvanic action, and a copious coagu-lation took place at the negative pole.

The decomposition of liquid albumen byvoltaic electricity takes place however in verydifferent ways according t q the power employed.When the power is comparatively high thecoagulation goes on rapidly at the negativepole and only slowly at the positive; whereaswith an extremely lory power, the coagulationis comparatively rapid at the positive surface,whilst an alkaline solution of albumen continuesto surround the negative pole. It would ap-pear also that gelatine is not precipitated bygalvanic action as albumen is; which mayafford an useful mode of analyzing and.sepa-rating a mixture of these two fluids, and alsoof distinguishing a solution of albumen in al-kali (such as exists in the serum of blood) fromreal jelly, which, when concentrated, it resem-bles, in having a gelatinous appearance. Thuson mixing a solution of isinglass with serumof blood and exposing the mixture to galvanicaction, the albumen of the serum was first se-parated by this means, after which an additionof galls detected the jelly of the isinglass ap-parently unaltered.

Professor Berzelius in his elaborate analysisof the blood d (which will be further noticedunder that article) finds that a solution ofalbumen, such as exists in the serum of blood,will readily dissolve many metallic salts par-ticularly the suboxyds of iron. This solutionis readily made, and is green when the blackoxyd is used and becomes yellow by exposure-

a-Phil. Journ. vol. 11. and 14. • b Thenard. An. Chim. tom. 67. ' Phil. Trans..for 1.809 & 1812.

* Medico-Clururgjcal Transactions, vol. 3.