836 SUMMARY OF CURRENT RESEARCHES RELATING TO 



whidi the tube passes, fasten the muslin tightly with thread to the 

 tube, and sink the l^glass to the bottom of the aquarium. On 

 exhausting the tube the glass will fill with water, and the aquarium 

 will in this way be emptied, the water passing through the muslin. 

 If a stoppage should occur the cause will in most cases be some 

 dirt having settled on the muslin. It is for this reason that a glass 

 with a wide mouth is recommended. 



Micro-chemical Test for Sodium.* — A. Streng proposes to em- 

 ploy uranium acetate as a test for sodium ; by its action on any 

 sodium solution, crystals of uranium sodium acetate are formed, which 

 are but sparingly soluble in water. They appear in the form of tetra- 

 hedra and the minute yellow crystals cannot be mistaken for the 

 rhombic crystals of uranium acetate, which separate out as the solu- 

 tion dries, on account of their action on polarized light. The reac- 

 tion is very sharp, as the double salt contains a very low percentage 

 of soda (6 • 6 per cent.). 



Micro-chemical Reaction of Solanine.j — J. Schaarschmidt gives 

 the following test for determining the presence of this alkaloid. 

 The section is laid in a drop of nitric acid or of not too concentrated 

 sulphuric acid, covered, and immediately placed under the Microscope. 

 A rose-red colour supervenes after a few seconds, especially if nitric 

 acid be employed. By this method the author found solanine in 

 Solanum tuberosum, especially in the sub-peridermal cells of the 

 tuber, and in the sub-epidermal cells of the stem and leaf-stalk ; also 

 in the coUenchyma of S. nigrum and Dulcamara, Capsicum annuum, 

 Lycopersicum esculentum, and Mandragora officinalis. The epidermis 

 of the sepals of Solanum nigrum is especially rich in solanine. 



Size of Atoms-I — Sir W. Thomson gives an estimate of the size 

 of atoms or molecules, founded on four lines of reasoning — (1) the 

 undulatory theory of light, (2) the phenomena of contact electricity, 

 (3) capillary attraction, and (4) the kinetic theory of gases — which all 

 lead to substantially the same estimate of the dimensions of molecular 

 structure. " Jointly they establish, with what we cannot but regard 

 as a very high degree of probability, the conclusion that, in any 

 ordinary liquid, transparent solid, or seemingly opaque solid, the 

 mean distance between the centres of contiguous molecules is less 

 than the l-5,000,000th, and greater than the l-l,000,000,000th of 

 a centimetre. 



" To form some conception of the degree of coarse-grainedness 

 indicated by this conclusion, imagine a globe of water or glass, as 

 large as a football, or say a globe of 16 centimetres diameter, to be 

 magnified up to the size of the earth, each constituent molecule being 

 magnified in the same proportion. The magnified structure would be 

 more coarse-grained than a heap of small shot, but probably less coarse- 

 grained than a heap of footballs." 



* Jahrb. f. Mineral., ii. (1883) p. 36.5. See Journ. Chem. Soc— Abstr., xlv. 

 (1884) pp. 366-7. 



- 1 Zeitschr. f. Wiss. Mikroskopie, i. (1884) pp. 61-2. 

 t Proc. Roy. Inst,, x. (1883) pp. 185-213 (11 figs.). 



