OF MIC110SCOPIC OBJECTS. 177 



the syringe. For this purpose we must procure small 

 earthenware or tin pots of the size required, which will 

 differ according to the kind of work to be done ; and to each 

 of these a loose lid should be adapted to protect it from 

 dust, &c. These pots must be allowed to stand in a tin 

 bath of water, under which a lamp or gas flame may be 

 placed to keep the temperature sufficiently high to insure the 

 perfect fluidity of tte mixture. The tin bath is, perhaps, 

 most convenient when made like a small shallow cistern; 

 but some close it on the top to place the pots upon it, and 

 alter the shape to their own convenience. 



8. We will now inquire into some of the materials which 

 are needed in this operation ; the first of which is size. 

 This substance is often used in the form of gltte, but it must 

 be of the very best and most transparent kind. To make 

 the liquid which is to receive the colours for the usual mode 

 of injecting, take of this glue seven ounces, and pour upon 

 it one quart of clean water; allow this to stand a few 

 hours, and then boil gently until it is thoroughly dissolved, 

 stirring with a wooden or glass rod during the process. 

 Take all impurities from the surface, and strain through 

 flannel or other fine medium. The weather affects this 

 a little as to its stiffness when cold, but this must be 

 counteracted by adding a little more glue if found too 

 liquid. 



9. Instead of glue, gelatine is generally used, especially 

 when the work to be accomplished is of the finer kind. The 

 proportions are very different in this case, one ounce of 

 gelatine to about fourteen ounces of water being sufficient. 

 This, like glue, must be soaked a few hours in a small part 

 of the cold water, the remainder being boiled and added, 

 when it must be stirred until dissolved. A good size may 

 be made by boiling clean strips of parchment for awhile, 

 and then straining the liquid whilst hot through flannel ; 

 but when the injections are to be transparent, it is of the 

 greatest importance that the size be as colourless as pos- 

 sible. For this purpose good gelatine must be employed, 



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