1892.] THE MICKOSCOPE. 107 



miscellaneous objects, etc., with directions for mounting them. 

 A dozen or more good mounts should be bought to serve as mod- 

 els. When neat mounts can be produced offer them for exchange 

 to the persons using the Exchange column. The American Mi- 

 croscopical Club, Troy, N. Y., receives suitable persons desiring 

 continuous membership. The Club circulates for examination 

 about 60 mounted objects, of w^ide diversity, each season, with 

 note-books containing a description of the preparations, methods 

 of mounting, and notes and comments by the members. An at- 

 tentive membership in the Club is a liberal microscopical educa- 

 tion. The Club year begins about October ist; an early applica- 

 tion should be made. 



7. The Cole Studies. What at'e they and ho%v shall I get 

 them ? — A Subscribe^'. 



Studies in microscopical science, issued by Arthur C. Cole, 

 consisted of a sewes of animal, vegetable, and mineral mounts, 

 accompanied by a full letter-press description, with lithographed 

 plates of each pr^aration. They were necessarily rather costly, 

 and their limited circulation was attended with pecuniary loss. 

 Their publication has been discontinued. American dealers may 

 still have some sets, or the author may be addressed : Mr. Arthur 

 C. Cole, St. Domingo House. Oxford Gardens, Notting-Hill, 

 London, W., England. 



8. Gold Crystals. Hozv are they 7nade? — S. W. C 



Use a strong solution of pure chloride of gold. Make a pool 

 of it in the centre of a glass slip. Cut a piece of zinc in the form 

 of a long triangle, bend this so the apex will reach to the centre 

 of the pool of gold solution, the base resting on the glass. Crys- 

 tals will radiate from the zinc in the centre of the pool. Wash 

 carefully with distilled water. When dry, cover. 



9. Diatoms a7id waste matter of the sa?ne specific gravity . 

 How can they be separated after using cdustic potash to break 

 down the earth? — P. ^. 



Caustic potash corrodes silex and should not be used on dia- 

 toms. Boil the material in w^ater until broken down. Then boil 

 with nitric acid, and nitric acid and a crystal of bicromate of 

 potash ; wash ; boil in w^ater with a morsel of soap ; wash. Re- 

 peat all processes again if the diatoms are not clean and bright. 

 Sand may be more or less completely removed by rotary washing 

 in a watch-glass, manipulating the glass so as to throw the 

 rolling sand to the edo:e, where it mav be easily removed. This 

 is a tedious process, but there is no other way, except to pick the 

 diatoms out with a mechanical finger. 



