1891.] MICROSCOPICAL JOURNAL. 59 



The powder was made to pass through a silk bolting cloth. It took 

 about half an hour to powder and sift a pound. — Norman N. Mason. 



'♦ Flower-Crystals " of Sugar. — This slide is prepared in accord- 

 ance with instructions given by L. A. Willson, Cleveland, Ohio, in the 

 )uly, '90, number of The Observer. 



Prepare two test tubes of saturated solutions of sugar ; one of alcohol, 

 the other of water. Then mix the two solutions in a third test tube, 

 and when thoroughly mixed, place a drop in the centre of a slide and 

 let it rest until it becomes a hard homogeneous mass. Then place the 

 slide, thus prepared, on the top of a student's-lamp shade. In the 

 course of a short time the flower crystals begin to develop. Leave the 

 slide in that position until crystals have developed over the whole mass. 

 The crystals are now very haid and permanent, and may be mounted. 

 — E. P. Bigelow. 



Cells and Cements. — Such objects as this fungus, or indeed any 

 dry-mounted objects, when designed for paraboloid or similar illumi- 

 nation, should be mounted in a cell of some solid substance. Never 

 use rings of wax, nor any cement like zinc white, asphalt, or gold size 

 for cells in dry mounting, and especially shun their use for all but the 

 very shallowest cells in any mounting. For thin cells use tin-foil or 

 lead-foil ; for thicker use sheet lead, brass, copper, or celluloid ; for 

 deep cells use bone, hard rubber, or brass rings. Cement the cells to 

 the slip with good, hard cement. When thoroughly dry spin a thin 

 coat of a quick-drying finish on the inside of the cell to cover its junc- 

 tion with the slip. When the last is completely dry mount the object, 

 using but little cement between the cover and cell. After long drying, 

 spin finishing cement on the outside of cell to cover junction of slide, 

 cell, and cover. When that is thoroughly dry, the mount is complete ; 

 and it will be permanent, free from '' sweating," and will never be 

 troubled with " running in" of the cement. — C. M. Vorce. 



\A^hite Zinc Cement. — The same old story. It is said that it 

 won't run ; if it don't, then it is because it has been appropriately 

 thrown out of the window. It has run in, in several of these slides. — 

 » » « 



Sections too thick. White zinc would not have run under if cells 

 had been properly made. — * * * 



More abuse of white zinc by careless and unskilful workers, who 

 blame the cement for their own lack of skill. I have several slides 

 which have been in my possession fifteen years (I don't know how old 

 they were when I got. them) and used hard, which are just as sound as 

 the day they were finished. In the present case the slides were prob- 

 ably mounted in haste before the cells were ready. They have also had 

 four years' travel and usage. — * * * 



The running in of white zinc and other cement is often due to the 

 surface of the glass, or to imperfect cleaning. I have mounted eight or 

 ten slides at the same time, of the same object, in same medium, and in 

 same manner in all respects ; and had perhaps one of the lot spoiled by 

 running in of cement and all the others stand perfectly for many years. 

 Some slips are slightly rough, some are striated, etc., and although they 

 may be clean the adhesion is not so perfect as to a smooth surface. I 

 think, however, more running in is caused by imperfect cleaning of the 

 slips. Sulphuric acid and bichromate of potash are very cheap, and it 



