MICROSCOPIC OBJECTS. 



Lesson XI. — Preparing Sections of 



Hard Substances for Photography. 



Many of the sections of hard substances, 

 such as bone, rock, etc., sold in the shops, 

 are too thick. Those prepared by the best 

 lapidaries cannot be excelled ; and if the 

 student can afford to pay the high price 

 charged for making these sections — from 2s. 

 to 2S. 6d. each — he is advised not to under- 

 take the labor and trouble of preparing them 

 himself. For, although the manipulator 

 may be skillful and patient, even when a 

 machine is used, cutting sections of rocks is 

 both tedious and laborious. 



There are many excellent machines in 

 the market specially devised for cutting 

 sections ; but they are all more or less ex- 

 pensive, and good work may be done by 

 using very simple appliances, which we shall 

 now proceed to mention. In the first place, 

 procure an iron plate, preferably cast iron, 

 about twelve inches square, and as thick as 

 can be obtained. Next, a Water- of- Ayr 

 stone, and one of harder texture, such as a 

 Washita stone. These may be obtained 

 at any tool shop. A Turkey stone is very 

 good for sections of bone. For grinding 

 do wn rocks, emery of various degrees of 

 fineness will be required — buy one pound of 

 medium coarse, one pound of medium fine, 

 and one pound of flour emery 



To grind down a rock section, proceed as 

 follows. Make a chip with a hammer 

 about one inch square, and not more than 

 one-eighth inch thick. Sedimentary rocks, 

 such as limestones, may be thicker. Rub 

 down the chip with coarse emery and water 

 on the iron plate, until one side is perfectly 

 flat. Remove the scratches by next rub- 

 bing the chip on a piece of plate-glass with 

 fine emery, and then polish with water on 

 the Water -of- Ayr stone; when quite 

 smooth, wash it well, and let it dry. Mean- 

 time put some old hard balsam on a glass 

 slip and warm it over a lamp until all the 

 more volatile parts of the balsam evaporate, 

 so that, on cooling, it becomes hard and 

 tough. Don't boil the balsam, and don't 

 continue the heat too long. When the 

 balsam is properly hard, heat the chip on a 

 metal plate, rub over it a little turpentine, 



and remelt the balsam ; lower one end of 

 the chip slowly into the balsam, and press 

 it down close to the glass slip. When the 

 balsam is cold, rub down the chip on the 

 iron plate with coarse emery until too thin 

 to bear further friction. Very hard rocks 

 may be brought down to the requisite thin- 

 ness on the iron plate alone, and will only 

 require a little polishing on a stone to re- 

 move the deeper scratches. Sections in- 

 tended for photography should be cut down 

 to the extreme of thinness, and all sec- 

 tions should be cut thin enough to read 

 through when placed on the page of a book 

 When the section becomes too thin to bear 

 any longer the friction of the coarse emery 

 wash it well, and grind it thinner on the 

 glass plate with fine emery, and finish off on 

 the Water-of Ayr stone. If the section is 

 strong enough to bear it, it should be re 

 moved from the slip on which it has been 

 ground, and mounted on a clean slip. 

 Warm the slide over the lamp sufficiently 

 to melt the balsam, and push the section off 

 with a needle into a cup of turpentine, and 

 wash it carefully with a small, soft brush. 

 Now pour a little balsam and benzole on the 

 clean slip, put the section ujon it, add a 

 little more balsam, and cover with a circle 

 or square of thin glass. 



Sections of bone or horn must be first cut 

 with a fine saw, and ground down in the 

 same way, only 7io emery must be used, 

 and the iron plate will not be required, as 

 the Water of- Ayr and Washita stones will 

 prove sufficient. Before such sections are 

 mounted, they should be soaked for a day 

 or two in balsam and benzole to render them 

 perfectly transparent. 



Sections of soft rocks, and sedimentary 

 rocks generally, are prepared and mounted 

 in the same way, only no emery must be 

 used, or it will imbed itself in the section 

 and cause false appearances under the mi- 

 croscope. Most sedimentary rocks can be 

 finished on the Water-of-Ayr stone. Some 

 very friable rocks, or substances such as 

 boiler incrustations, which readily disinte- 

 grate on the grinding-stone, must first 

 undergo a preliminary hardening. Two 

 hardening solutions lae generally made use 



