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-WatTER 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 ewtra adhesive 
. gum-water, which is made with the addition of isinglass, 
thus :—Dissolve two drachms of isinglass in four ounces of 
distilled vinegar; add as much eum 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. ne 
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 partly on the 
