OF MICROSCOPIC OBJECTS. 47 



It must be used whilst hot, and as long as it retains even 

 slight warmth can be readily moulded into any form. It is 

 often employed in making shallow cells for liquids, as before 

 mentioned. 



GUM- WATER is an article which nobody should ever be 

 without; but labels, or indeed any substance, affixed to 

 glass with common gum, are so liable to leave it spon- 

 taneously, especially when kept very dry, that I have lately 

 added five or six drops of glycerine to an ounce of the gum 

 solution. This addition has rendered it very trustworthy 

 even on glass, and now I never use it without. Ten grains 

 of moist sugar to each ounce of gum solution will also 

 answer equally well. This solution cannot be kept long 

 without undergoing fermentation, to prevent which the 

 addition of a small quantity of any essential oil (as oil of 

 cloves, &c.), or one-fourth of its volume of alcohol, may be 

 made, which will not interfere in any way with its use. 



There is what is sometimes termed an extra adhesive 

 {rum-water, which is made with the addition of isinglass, 

 thus : Dissolve two drachms of isinglass in four ounces of 

 distilled vinegar; add as much gum arabic as will give it 

 the required consistency. This will keep very well, but is 

 apt to become thinner, when a little more gum may be 

 added. 



I may here mention that Messrs. Marion have lately 

 brought out a cement for the purpose of mounting photo- 

 graphs, which is very adhesive, even to glass. I find it 

 useful in all cases where certainty is requisite ; as gummed 

 paper is liable in a dry place to curl from the slides, as 

 before mentioned. 



All these, except one or two, are liquid, and must be kept 

 in stoppered bottles, or, at least, as free from the action of 

 the air as possible. 



When any two substances are to be united firmly, I have 

 termed the medium employed " a cement ;" but often the 

 appearance of the slides is thought to be improved by 

 drawing a coloured ring upon them, extending parti}- on the 



