62 HOW TO WORK 



may be effected with an ordinary sharp-pointed file if the end be 

 moistened from time to time with a little turpentine. The operation 

 is of course more quickly performed with a drill, the point of which 

 has been rendered very hard. 



122. Ceiin-iitins Glass together with Marine Clue. The surface 

 of glass to which a cement is to be applied should always be 

 roughened by grinding, as the cement adheres much more intimately 

 to a rough surface than to the polished glass. 



Glass is cemented together with marine glue, and in making large 

 built glass cells, the edges are united by means of the same substance, 

 which can now be readily obtained. Formerly gold size, Canada 

 balsam, and other cements were employed, but these are all inferior 

 to marine glue. 



The manner of applying the marine glue to the glass has been 

 already alluded to. The glass must always be warmed upon a flat 

 brass or iron plate, so that the heat may be applied gradually and 

 equally. It must not be touched with cold fingers, but must be held 

 with wooden forceps, or with ordinary forceps, the extremities of 

 which have been protected with pieces of cork, in the manner 

 described in 82. 



When the pieces of glass of which the cell is to be composed are 

 warm enough, a little glue cut into small pieces is allowed to melt in 

 the position in which the glass is to be fixed. When it is melted, the 

 glass is applied and pressed down upon a deal board, so as to squeeze 

 out as much marine glue as possible and make a good joint. 



The student should make for himself a plate-glass stage. A piece 

 of thin plate plass is cut about four inches by two. The edges are 

 to be ground smooth and a narrow strip of glass cemented to one 

 edge with marine glue. This is to support the ordinary glass slide. 

 A glass stage of this description protects the microscope, especially 

 when acids or corrosive fluids are used, fig. 97, pi. XVII. 



123. Cleaning oft' Superfluous Glue. While the slide is yet warm, 

 much of the glue may be scraped off with an old knife and small 

 chisel, pi. XVI, fig. 93, after which a little solution of potash (the 

 liquor potasses of the shops) will soften the remainder. It may then 

 be very readily removed with the aid of soap and water and a 

 nail brush. Or the whole cell may be soaked in equal parts of liquor 

 potass3e and water, but we must bear in mind that if the cell be 

 soaked for too long a time in strong solution of potash, there is 

 danger of the glue between the glass being softened. The potash must 

 always be carefully washed away, to prevent the chance of the glue 

 being softened after the cell is complete. 



124. Cells made of Thin Glass. The neatest and most perfect 



