218 Queries. 
417.—Zine Cement.—There must be some fault in the compo- 
sition of the zinc cement which does not harden properly or 
become white when slides are ringed with it. If such is the case, 
better discard it and purchase a fresh bottle. Or could it be that 
the cement has not been sufficiently shaken up before being used ? 
If so, the zinc white would be at the bottom of the bottle, and 
the varnishing would be done with a mixture of balsam and 
benzole, or some similar compound. I keep a piece of steel wire, 
like a stout knitting-needle, about one-eighth of an inch thick, for 
the sole purpose of stirring up and mixing well the contents of my 
zinc-white cement bottle before ringing slides ; and I may mention 
that just now I am very near the bottom and end of a bottle, and 
it works as pleasantly and finishes as satisfactorily as when I first 
opened it. From time to time it is necessary to add a little 
fresh benzole, to make up for the loss by evaporation. 
H.. W.. LEriysMea 
419.—Mounting in Balsam—The cause of air getting under 
the cover-glass in balsam mounts when the spring clip is removed, 
and the superfluous medium is being scraped off, is due to the clip 
having exerted too great pressure. I once met with the same 
annoyance, but when I discovered the cause I gave up the ordi- 
nary wire clips, and adopted the Sczexce Gossip spring-clip board, 
which I constructed for myself with a piece of pine board, a few 
small screw-nails, and some crinoline steel, and now I never meet 
with mishaps. It gives sufficient, equal, and gentle pressure. But 
besides this, I always, when mounting in balsam, follow Cole’s 
directions, and place the object in some balsam on the cover, 
where it remains for some hours till the benzole or chloroform has 
sufficiently evaporated from the balsam, when it is placed in 
position on the glass slip, which must be previously warmed. For 
further instruction, see Cole’s ‘Method of Microscopical 
Research.” H. W, Lerr visas 
Queries. 
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430.—Portland Cement.—Can anyone say how this is manufac- 
tured ? I understand it is somewhat in the following way :—Caustic 
