106 Mr. Roberts on the Action of Isinglass 



The properties of gelatine must therefore be considered, 

 it being analogous to pure Isinglass. 



Gelatine is distinguished from all animal principles, by 

 its ready solubility in boiling water, and also in most of the 

 diluted acids, which form excellent solvents for it. 



Gelatine is perfectlyinsoluble in alcohol, and almost equal- 

 ly so in cold water. It is precipitated from its solutions by 

 infusions of tannin. 



An infusion or tincture of galls, will precipitate it from 

 its solution in 5000 times its weight of water. 



These are briefly the properties of gelatine, or pure Isin- 

 glass, which should be borne in mind in operating on it. 



A great variety of Isinglass is offered for sale, at a range 

 of prices from three, to sixteen shillings per pound ; and 

 the relative value of each kind may be known by the follow- 

 ing tests : 



In the first place, Isinglass should remain unchanged by 

 being steeped in spirit of wine or alcohol, from 50° to 60° 

 over proof, in which gelatine (the chemical principle of 

 Isinglass) is insoluble. The alcohol, or spirit of wine, in 

 which the isinglass has been steeped, should then be tried 

 with a few drops of tincture of galls ; if the liquor remain 

 clear and unchanged, it is much in favour of the character 

 of the Isinglass. If, on the other hand, the tincture of galls 

 causes a precipitate from the alcoholic liquor, the Isinglass 

 is not pure, as it contains something more than pure gelatine. 



Different samples of Isinglass which have remained un- 

 changed in alcohol or spirit of wine, should also be tried by 

 the two following methods, before an opinion can be given 

 as to their relative value. Try given weights of each sample 

 (one-eighth of an ounce for instance) in three ounces of water 

 by measure) in separate vessels ; bring them gradually to a 

 boil, occasionally stirring each sample. While hot, strain 

 the different solutions through muslin, into separate vessels. 

 In proportion to che quantity of undissolved matter left 

 upon each strainer, may the solubility of the different sam- 

 ples be ascertained ; that which leaves the least residuum 

 will form, when cold, the strongest jelly, upon which the 

 clearing property of Isinglass depends. The remaining trial 

 to which the different samples are to be submitted, is the 

 last and most decisive one. Equal weights of each sample 



