CEMENTS, VARNISHES, AND CELLS. 245 



mounts, which were strengthened by a ring of varnish, were but 

 little affected, while those not so protected suffered greatly. 

 None of the wax cells made, as described later on, lost their 

 covers or separated from the slide, while a large number of those 

 made by cementing rings of wax to the slide were spoiled. 

 Shellac, not backed up by a tougher cement, gave out in almost 

 every instance. 



Gold size has been a favourite cement with me for a long 

 time. Some eight years ago I procured a number of bottles 

 from Messrs. Queen & Co., and some that is still left seems 

 stronger than when first bought. Gold size is simply linseed oil 

 rendered very ^'- drying^ There are, however, a number of 

 different formulae for its preparation, and when you find a sample 

 that is of more than ordinary worth it is well to lay in a supply. 

 The same holds true of all such material as is not liable to 

 deteriorate with age. Gold size hardens by oxydation, and very 

 slowly at that ; so a sufficient length of time must be allowed for 

 each coat to become hard. If it were not for the slowness with 

 which it hardens it would make an admirable cell. As it must be 

 applied in very thin layers it takes too long to make cells of any 

 great depth, and unless they are carefully made they will eventually 

 break down. I use gold size for dry mounts, to attach metal 

 cells, to " pack up " a more brittle cement, and, in fact, in all 

 cases where it is possible to do so. 



Another cement, which works well with me, is Shellac. It 

 must be the genuine article, and not the resin compound that is 

 frequently sold for it. Shellac I prepare as follows : — Put a few 

 scales of orange lac in a wide-mouthed bottle and cover with 95 

 per cent, alcohol. The bottle is placed in a water-bath, and a 

 gentle heat applied until the shellac is dissolved, when it is filtered 

 through muslin or absorbent cotton, previously moistened with 

 alcohol. If too thick, add more alcohol and continue the heating 

 for a short time. The shellac must be thin, as if thick it does not 

 adhere as well. It will in course of time become thick from the 

 evaporation of a portion of the alcohol, when it should be 

 prepared afresh. The rule that cements and varnishes are 

 deteriorated by being thinned after they have become thick by 

 evaporation or oxidation has few, if any, exceptions. 



