338 THE AMERICAN MONTHLY [Dec, 



low them a day to settle, as with the small quantities that you 

 use, it is very difficult to filter without losing the greater part 

 by absorption, which necessitates making a much larger quanti- 

 ty than is necessary. 



Take a clean slide and place it in the card-board guide and 

 drop a small quant ty of the solution of tartrate of soda in 

 the centre as near as possible, with a small pipette ; have the 

 hot plate heated beforehand, the flame of the spirit lamp being 

 about two inches from the brass plate; place the slide on the 

 hot plate and leave it about a quarter of an hour to thoroughly 

 heat. It wi!l dry to a thin film-like gelatin. No sign of crys- 

 tallization appealing, place in a position to be free from dust 

 and examine every day so as to observe when crystallization 

 commences. In about three days you will perceive some 

 small discs on different parts, which after the lapse of a few 

 more days will spread over the who^e of the film. I have tried 

 mounting some before the crystalizati')n had covered the whole 

 of the slide, as I thought they looked more brilliant when a 

 portion of the ground was seen, but found that after a few days 

 the crystallization had spread over the the whole space, although 

 they were mounted in castor oil. 



This is a very handsome preparation and is well worthy of a 

 p^ace in the cabinet. Th*^ discs are v-^ry similar to, and as 

 brilliant as Salicine, showing well the cross, and being much 

 improved by the selenite film. 



Castor oil is the l)est general medium by far for mounting 

 crystals in. 1 have not yei found any salts that are affected by 

 it, unless a lengthened time may cause some change. I have 

 not found it easy to get rid of air-bubbles in th^ case of crystals 

 that contain interstices, but will try what the air-pump will do 

 in this case. 



It is very easy to use and to seal up, and never contains air- 

 bubbles in itself as balsam frequently does. I press a couple of 

 drops from the tube and lay the cleaned glass cover carefully 

 on the side that contains the highest ridge, so as to make sure 

 of not including any air; clip the slide, and remove the excess 

 of oil with a soft brush, beins careful not to l^t the hairs get 

 under the cover. Wipe the brush from time to time on a bit 

 of blotting paper or rag. When the bulk of the oil is removed, 

 dip the brush in alcohol and clean as much off as possible. On 



