8 4 



MOUNTING AND LABELING. 



ARRANGING AND MOUNTING MINUTE OBJECTS- 



\ 194. Minute objects like diatoms and the scales of insects may be arranged in 

 geometrical figures or in some fanciful way either for ornament or more satisfac- 

 tory study. To do this the cover-glass is placed over the guide. This guide for 

 geometrical figures may be a net-micrometer or a series of concentric circles. In 

 order that the objects may remain in place, however, they must be fastened to the 

 cover-glass. As an adhesive substance, liquid gelatin (\ 194) thinned with an 

 equal volume of 50 per cent, acetic acid answers well. A very thin coating of this 

 is spread on the cover with a needle or in some other way and allowed to dry. 

 The objects are then placed on the gelatinized side of the cover and carefully got 

 into position with a mechanical finger, made by fastening a cat's whisker in a 

 needle holder. For most of these objects a simple microscope with stand (Fig. 8) 

 will be found of great advantage. After the objects are arranged, one breathes 

 very gently on the cover-glass to soften the gelatin. It is then allowed to dry and 

 if a suitable amount of gelatin has been used, and it has been properly moistened 

 the objects will be found firmly anchored. In mounting, one may use Canada 

 Balsam or mount dry on a cell (£§ 170, 176). See Newcomer, Auier. Micr. Soc's 

 Proc. 1886, p. 128 ; see also E. H. Griffith and H. L. Smith, Amer. Journal of Mi- 

 cros., iv, 102, V, 87; Amer. Monthly Micr. Jour., i, 66, 107, 113. Cunningham, 

 The Microscope, viii, 1888, p. 237. 



MICRO-CHEMISTRY AND CRYSTALLOGRAPHY— EXPERIMENTS. 



§ 196. The student of science and especially chemistry so frequently requires a 

 knowledge of the appearance of minute crystals to aid in the determination of an 

 unknown substance or for his information in studying objects where crystals are 

 liable to occur, that a few experiments have been introduced to give him a start in 

 preparing and permanently mounting some of the common crystals. 



It is recommended that the crystals be made in several ways, that is from alco- 

 holic solutions, aqueous solutions saturated and dilute, by spontaneous drying and 

 crystallization and by rapid crystallization by the aid of heat. The modifications 

 in crystallization under these different methods of treatment are frequently very 

 striking. 



In every case the student is advised to study the appearance of the crystals in 

 the "mother liquor. " As a rule their characteristics are more clearly shown in 

 the "mother liquor" than under any other conditions. 



It is of very great advantage to examine all crystalline forms with polarized 

 light (j 156). 



\ 197. Determination of the Character of th2 Solid Sediment in Water. — Take 

 some of the sediment from a filter or allow a considerable volume of water to 

 stand in a tall glass vessel to deposit its sediment. Take a concentrated drop of 

 this sediment and mount it on a slide under a cover-glass. Study the preparation 

 with the microscope. Probably there will be an abundance of animal and vegeta- 

 table life as well as of solid sediment. Put a drop of dilute sulphuric acid 

 {Aciduni sulphuricum dilutum, i. e., strong sulphuric acid 1 gram, water 9 grams) 

 at the edge of the cover and at the opposite edge a small piece of the Japanese 

 paper (PI. V, Fig. 49). The acid will gradually diffuse, and if the solid particles are 

 carbonate of lime, minute bubbles will be seen to be given off. If they are silica 

 or clay no change will result. Sulphuric acid is recommended for this, as the mi- 



