Mr Fearcey on Preparing Thin Sections of Friable Bocks, etc. 297 



liquid, and is then ready for immediate use. I find nothing 

 else will dissolve the gum copal so well ; other things which 

 were tried only caused it to form a thick white gelatinous 

 mass, quite unfit for the purpose required, and care should 

 always be taken to procure the best gum copal, as some 

 kinds dissolve more readily than others. 



The substance required to be hardened should be first 

 well dried in a porcelain dish (PL XI., Fig. 4, a, h) upon a hot 

 iron plate placed upon a tripod stand over the flame of an 

 ordinary Bunsen burner. The material is next placed in a 

 porcelain crucible (PI. XL, Fig. 3, a), varying in size according 

 to the amount of substance required. About twice the volume 

 of the solution of gum copal and ether should then be poured 

 upon it, always taldng care to press the stopper of the bottle 

 well in afterwards. This part of the work should never be 

 done near a fire or gas light. 



The crucible containing the substance is next placed upon 

 the hot iron plate, care being taken to have a slow or 

 moderate heat at first, and to allow the mass to simmer till 

 the ether has partly evaporated, when a greater heat may with 

 safety be applied. If the substance be a fine sand or ooze 

 of any kind, it must be well stirred with a needle-point or 

 small knife, otherwise it will stick to the bottom of the 

 crucible, and not allow the gum copal to mix with it. If the 

 specimen to be hardened be a soft, porous, or decomposed 

 rock, it will only be necessary to turn it a few times, so that 

 the solution may thoroughly penetrate all the pores. Great 

 care must also be taken during this part of the operation, as 

 the cement is of a very inflammable nature, and therefore 

 caution is essential not only in stirring, in consequence of 

 the gum having a tendency to stick to the sides of the 

 crucible, but also in removing the stirring-needle to avoid 

 contact with the flame. To prevent overturning the crucible, 

 a strip of stout tin, slightly narrower than the depth of the 

 crucible, and bent round so as to make one end overlap the 

 other, so that the crucible fits in firmly (PL XL, Fig. 3, h), is 

 very useful. This keeps it perfectly steady, and can be taken 

 off after the substance has been boiled sufficiently. 



After nearly all the ether has evaporated, the substance, if 



