MICRO-CRYSTALLIZATION. 27 
mixing both together, place a drop upon a cold slide, gently warm 
until opal, oyster shell-like crystals begin to appear: instantly then 
remove from the warmth, and generally the appearance of the 
slide is improved if now it is cooled rapidly by placing it upon a 
cold surface; but this is a matter requiring more attention and 
experiment than, has yet been given to it, and though I cannot 
always depend upon getting this precise form, when obtained, 
they are very interesting, shewing a combination of the broad 
crystallization of the tartaric, and the needle-like crystals of the 
gallic acid. This combination when produced needed a name, 
and upon recommendation of some chemical friends, it was 
designated Gallo-tartaric Acid. 
Pyrogallic Acid, a substance at the present time well-known to 
Photographers and Photo-micrographers, next claims our attention, 
and will yield at least two good forms to the student of Crys- 
tallography. By making a cold saturated solution of this acid in 
water and placing a drop upon the slide, it will very quickly cover 
the spot with long needle-shaped crystals; but if a very minute 
shower of some insoluble foreign substance be allowed to fall upon 
the solution when on the slide, the effect is grand,—each minute 
speck forming a nucleus around which the needle crystals gather, 
forming, if examined with a selenite slide, so resplendent an object 
that no words of mine can adequately describe it. 
Hippuric Acid will also be found worthy of all the attention 
that can be given to it, and upon experiment would probably 
yield many varied results. I will mention two I have produced, 
known respectively as Circular and Floral Crystals. 
Circular, or as they are frequently called, Wheel Crystals, may 
be obtained by making a strong solution in pure alcohol ; in this 
case methylated spirit not answering sufficiently well. Drop on a 
warm slide a little of this solution and immediately hold over a 
spirit lamp, removing the slide from warmth directly the crystals 
begin to form; but should the crystallization stop, it can be 
caused to recommence by again warming. 
Floral Crystals may be obtained from the same solution, but it 
must be dropped upon a cold slide; and if the slide is gently 
waved about to evaporate the alcohol, the floral crystals will form ; 
and the suggestion may be offered, though I have never put it to 
experiment, that if a rotary movement is given to the slide the 
crystals, as they form, will be a combination, possibly taking the 
character of circular florets. ; 
As a conclusion to my selection of acid crystallizations, your 
attention must be directed for a moment to Citric Acid, which, 
although a most difficult form to produce, is so strikingly beautiful 
that it deserves the expenditure of all necessary time and trouble. 
The most successful plan with this acid is to make a very strong 

