PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS. 197 



be here given; 1 but those special details of management which par- 

 ticular substances may require, will be given when these are respectively 

 described. The first thing to be done will usually be to procure a section 

 of the substance, as thin as it can be safely cut. Most substances not sili- 

 ceous may be divided by the fine Saws used by artisans for cutting brass; 

 and these may be best worked either by a mechanical arrangement such 

 -as that devised by Dr. Matthews, 2 or, if by hand, between ' guides,' such 

 as are attached for this purpose to Hailes's and some other Microtomes. 

 But there are some bodies (such as the Enamel of Teeth, and Porcellane- 

 ous Shells), which, though merely calcareous, are so hard as to make it 

 very difficult and tedious to divide them in this mode; and it is much the 

 quicker operation to slit them with a disc of soft iron (resembling that 

 used by the Lapidary) charged at its edge with diamond-dust, which disc 

 may be driven in an ordinary lathe. Where waste of material is of no ac- 

 count, a very expeditious method of obtaining pieces fit to grind down, 

 is to detach them from the mass with a strong pair of ' cutting pincers, 

 or, if they be of small dimensions, with ' cutting pliers;' and a flat sur- 

 face must then be given to it, either by holding them to the side of an 

 ordinary grindstone, or by rubbing on a plate of lead (cast or planed to a 

 perfect level) charged with emery, or by a strong-toothed file; the former 

 being the most suitable for the hardest substances, the latter for the 

 toughest. There are certain substances, especially Calcareous Fossils of 

 Wood, Bone, and Teeth, in which the greatest care is required in the 

 performance of these preliminary operations, on account of their extreme 

 friability; the vibration produced by the working of the saw or the file, 

 or by grinding on a rough surface, being sufficient to disintegrate even a 

 thick mass, so that it falls to pieces under the hand; such specimens, 

 therefore, it is requisite to treat with great caution, dividing them by the 

 smooth action of the wheel, and then rubbing them down upon nothing 

 rougher than a very fine 'grit/ or on the 'corundum-files' now sold in 

 the tool-shops, which are made by imbedding corundum of various 

 degrees of fineness in a hard resinous substance. Where (as often hap- 

 pens) such specimens are sufficiently porous to admit of the penetration 

 of Canada Balsam, it will be desirable, after soaking them in turpentine 

 for a while, to lay some liquid balsam upon the parts through which the 

 section is to pass, and then to place the specimen before a fire or in an 

 oven for some little time, so as first to cause the balsam to run-in, and 

 then to harden it; by this means the specimen will be rendered much 

 more fit for the processes it has afterwards to undergo. It not unfre- 

 quently happens that the small size, awkard shape, or extreme hardness 

 of the body, occasions a difficulty in holding it either for cutting or grind- 

 ing; in such a case, it is much better to attach it to the glass in the first 

 instance by any side that happens to be flattest, and then to rub it down 

 by means of the ' hold ' of the glass upon it, until the projecting portion 

 has been brought to a plane, and has been prepared for permanent attach- 

 ment to the glass. This is the method which it is generally most conve- 

 nient to pursue with regard to small bodies; and there are many which 

 can scarcely be treated in any other way than by attaching a number of 



1 The following directions do not apply to Siliceous substances; as sections of 

 these can only be prepared by those who possess a regular Lapidary's apparatus, 

 and have been specially instructed in the use of it. 



2 " Journ. Quekett Microsc. Club," Vol. vi. (1830), p. 83. 



