698 RECOBD OF CURRENT RESEARCHES RELATING TO 



exj)ensive cement may, however, be made by dissolving 10 grains of 

 gum-ammoniac in 1 ounce of acetic acid (No. 8), and tben by adding 

 to this solution 2 drachms of Cox's gelatine. The resulting liquid 

 flows easily from the brush and is waterproof, especially so if, after 

 the ring has set, it is brushed over with a solution of 10 grains of 

 bichromate of potash in 1 ounce of water. But what especially 

 recommends this cement is its great adhesive power to glass, even if 

 there should be a little glycerine on the edge of the cover. After the 

 gelatine ring is dry, any other cement may be employed to cover it, 

 according to the fancy of the preparer. 



When a considerable number of different objects are being pre- 

 pared at the same time, it is of great imjiortance to be able to tell 

 one from the other, so as finally to label them correctly without 

 subjecting them to a careful microscopical examination, A pajier 

 label, under the frequent necessary handling of the slide, becomes 

 soiled, and the writing frequently illegible ; while a figure or even a 

 full label, written with a pen upon the glass slide, will remain intact 

 throughout the manipulations of cleaning and ringing, and at the 

 same time can easily be removed by a little rubbing with a rag dipped 

 in water. 



In order to facilitate the finding of slides in a large collection, 

 it is advisable to place the label bearing the name of the object 

 always on the same end, and if two labels are used to place the one 

 with the prejjarer's name on the right hand, and the other bearing the 

 description of the object on the left." 



Cleaning Cover-glasses.* — Dr. E. U. Piper, of Chicago, has 

 suggested a very simple method of cleaning cover-glasses without 

 breaking them. Upon a glass plate 2x3 inches are cemented, in 

 the form of a V, two thin strips of glass. A cover-glass may be laid 

 U2)on the glass plate, inside of the V, and cleaned by rubbing freely, 

 being held in position from slipping by the sides of the V. 



Preparing Sections of Coal. — Mr. E. T. Newton, the Assistant- 

 Naturalist of the Geological Survey, who has successfully examined 

 the microscopical structure of many varieties of coal, gives f the follow- 

 ing description of the methods employed by him in making his 

 preparations : — 



" One important point to be noticed at the outset is that nothing 

 like emery powder can be used for the grinding, as the grains embed 

 themselves in the softer substance of the coal, and, when the section 

 is finished, will be seen as minute brip;ht sj^ots, thus giving to the 

 section a deceptive appearance. For the rough grinding an ordinary 

 grindstone may be used, and for the finer work and finishing a strij) 

 of ' pumice-stone ' (or corundum stick), and a German hone (or Water- 

 of-Ayr stone). The form of these which has been fouud most con- 

 venient is a strip about 1^ inch wide and about G inches long ; the 

 thickness is immaterial : one of the broader surfaces of these must be 

 perfectly flat. 



* ' Ain. Nut.,' xlv. (1880) p. 465. 



t F. Rutlcy's ' Study of Rocka ' (8vn, LoJiduii, 187'J). \\ 71. 



