224 SELECTION AND USE 



DAMAR CEMENT. This is a mixture of equal parts of damar 

 tarnish and gold size, mixed together. It should stand for 

 some time before being used. It is said to be very excellent. 

 It is very tough, and serves well as an outer coating over such 

 brittle cements as shellac and sealing wax varnish. 



MARINE GI/UE. This is undoubtedly the strongest cement 

 in use for joining pieces of glass or glass and metal together. 

 Skilful microscopists make great use of it; beginners do not 

 find it so easy to manage as some others. In using it, the 

 simplest method is to cut it in small pieces, lay it on one of the 

 surfaces that are to be joined, melt it by heat, and apply the 

 other surface, making sure of perfect contact by rubbing the 

 two pi eces upon each other, if they will allow of it. Marine 

 glue may be obtained from most dealers in microscopes. 



The cement known as liquid glue, is simply a solution of 

 shellac in alcohol. 



For attaching labels, paper covers, etc., to the slides, nothing 

 is better than good dextrine. After having mixed the dextrine 

 with water to the proper consistence, add six drops of glycer- 

 ine to the fluid ounce of dextrine. This will prevent the labels 

 or covers from cracking off. 



Having provided himself with the necessary tools and mater- 

 ials, the next step is to learn how to use and apply them, and this 

 will probably be most easily taught by describing a few char- 

 acteristic examples. And first of all, selecting the most easily 

 mounted of all objects, we commence with the scales on the 

 butterfly's wings. Having prepared a cell of proper size, and 

 allowed it to dry, the first step is to select a cover to suit it, 

 and give a final cleaning to both slide and cover. When every 

 particle of dust has been removed, breathe gently on the slide, 

 and press the wing lightly against it, and within the cell. A 

 large number of scales will at once adhere to the slide, and 

 the next step is to attach the cover. Place the slide on the hot- 

 plate, (which must not be too hot, however,) and when it is 

 thoroughly dry, and the cement somewhat soft, lay the cover 

 on by means of the cover forceps. Press it into contact with 

 the cement, and the operation is completed. It is not difficult 

 to see when the cover and the cement are in perfect contact, 



