CEMENTS. 293 



It is still further improved by adding to the 

 isinglass, previous to its solution in spirits, one- 

 third of its weight of gum ammoniac. Expose the 

 mixture to a boiling heat, until the isinglass and 

 gum are dissolved, and until a drop of the compo- 

 sition become stiff instantly as it cools. It will at 

 any future time melt with a degree of heat little 

 exceeding that of the human body, and, in conse- 

 quence of so soon becoming stiff on cooling, forms 

 a very valuable cement for many purposes, particu- 

 larly for the very nice and delicate one of fixing on 

 the antennas, legs, &c. of insects in cabinets of na- 

 tural history. The easy melting of this cement is 

 no objection to its use in cases where the articles 

 themselves may afterwards be exposed to moderate 

 heat ; for it owes this property only to the presence 

 of the spirit which evaporates soon after it has been 

 applied. When used to join broken glass or china, 

 the pieces to be joined should be previously warmed. 

 Immersion in hot water will give them a sufficient 

 degree of heat. Wipe off the water before applying 

 the cement, which may be laid on with a pencil ; 

 then press the pieces together, binding them with 

 a string, or bit of soft wire, if necessary. 



This isinglass glue is far preferable to common 

 glue for nice purposes, being much stronger, and 

 less liable to be softened either by heat or moisture. 



Parchment Glue. 



Take one pound of shreds of parchment, or vel- 

 lum, and boil it in six quarts of water till the quan- 

 tity be reduced to one quart ; strain off the fluid 

 from the dregs, and then boil it again till it be of 

 the consistence of glue. 



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