zo6logy and botany, microscopy, etc. 527 



affected in form or appearance during an experiment like that just described. 

 Occasionally, however, the bubbles in a water-cavity are excited into lively 

 motion and repelled into the farthest side of the cavity by the sudden 

 application of heat. In place of a rubber tube, the application of a warm 

 wire, glass rod, or of the burning end of a cigar, a little below the slide, 

 may be substituted to produce the same effects — or even the direct applica- 

 tion of the warm end of one's finger to the bottom of the slide for a few 

 minutes. 



The author gives an interesting description of the cavities and their 

 contents, and the phenomena which they present. 



Identification of Alkaloids and other Crystalline Bodies by the 

 Microscope.* — Mr. A. P. Smith considers that whilst the number of cases 

 in which a crystalline substance can be identified by the Microscope alone 

 is extremely limited, yet, as a test of purity, microscopical investigation has 

 a very wide application. When we are dealing with a substance that, when 

 pure, crystallizes in a different form from any particular solvent, it is 

 manifest that any departure from that form would lead to the suspicion of 

 adulteration. If we take such a substance as bark, or opium, it is quite 

 possible to distinguish from each other the various alkaloids which it 

 contains. Besides the form assumed by the free base, it is of importance to 

 convert it into a salt, as there is frequently a marked departure in the form 

 of the crystals, e. g. quinidine and quinidine sulphate, cinchonidine and 

 cinchonidine sulphate. There may be cases in which the salt and the base 

 possess the same crystalline form. 



Some experience is necessary in selecting the most suitable solvent from 

 which to crystallize an alkaloid, as the duration of the evaporation may 

 have a marked effect upon the form of the crystals. In some cases evapora- 

 tion may be accelerated by the aid of heat ; in others, such a proceeding is 

 fatal to success. The addition of alcohol to ether, and of water to alcohol, 

 appears to be the best means of retarding the process when necessary. 



Polarized light should be employed to view the crystals, either with or 

 without a selenite plate. Here, again, the duration of evaporation has a 

 marked effect, also the strength of the solution. If the substance is 

 deposited in a thin film, it may be altogether invisible without polarized 

 light. Thick crystals frequently produce colour without the selenite, and 

 those that are very thick may depolarize without any coloration. This 

 being borne in mind, no difficulty is experienced in practice, as it is easy to 

 compare with an alkaloid of known purity crystallized under the same 

 conditions. 



Figures are given of various substances crystallized under the best con- 

 ditions, with the name of the solvent and the linear magnification, together 

 also with a list of alkaloids and a description of the forms of the crystals. 



Caepene, a. — Nuovo process© d' analisi delle materie coloranti, introdotte nei vini 



ed altri liqoidi ed in sostanze alimentari solide, fondato sul coloramento del micro- 



organismi. (New process of analysing the colouring matters introduced into wine 



and other liquids and in solid alimentary substances, founded on the staining of 



the micro-organisms.) 11 pp. and 1 pL, 8vo, Torino, 1887. 



Cole, A. C. — Studies in Microscopical Science. Vol. IV. Sees. I.-IV. Nos. 8-9 (each 



4 pp.). 



Sec. I. Botanical Histology. No. 8. Studies in Vegetable Physiology. VIII. 



Defoliation (Plate 8. A fallen leaf. Virginia Creeper : Ampelopsis hcderacea. 



Long. sec. through the stem and base of petiole.) No. 9. Digestive Glands. 



* Journ. Postal Micr. Soc, v. (1886) pp. 210-8 (2 pis.), from ' The Analyst.' 



