920 SUMMARY OF OURBENT RESEARCHES RELATING TO 



Herr Assmann took the opportunity, with a power of 400, to test 

 Aitken's theory as to the condensation of the vapour in the air to 

 solid particles. The smallest drops evaporated slowly in from 10 to 

 15 seconds under the Microscope, without leaving the slightest trace 

 of any residue. A particle of the size of • 005 mm. could not have 

 escaped observation under the favourable conditions of light and 

 during the many hundred separate observations. 



At 2 o'clock the wind veered from W. to N.W. and became cooler, 

 the air being 1° colder, the relative dampness greater, and the clouds 

 higher and thicker. Under the Microscope large drops of a diameter 

 of • 04 mm. were almost exclusively to be observed, and they lay so 

 close that the entire field of view was covered with water. At 

 3 o'clock a fine rain fell. 



In a subsequent ascent of the Brocken on 31st December, under- 

 taken for the purpose of studying the formation of hoar-frost, 

 Herr Assmann fixed his Microscope by allowing it to freeze to a 

 lump of ice, attached a fine woollen hair to the glass slide, and soon 

 saw very small drops of water fall on the glass, when the summit was 

 quite hidden by clouds. These drops were all liquid in spite of the 

 temperature being at — 10° C. and they evaporated comparatively 

 quickly. The smallest forms predominated. Not a single crystal of 

 ice or snowflake was visible among the drops of water. Small drops 

 that did not evaporate in 5-10 seconds froze to ice of the same size. 

 These were entirely transparent and devoid of air. 



Micro-cliemical Test for Brucin and Stryclmiii.*— Dr. O. Lindt 

 has examined the seeds of Strychnos nux-vomica and Strychnos ignatii 

 micro-chemically for the above alkaloids. Nitric acid and Erdmann's 

 reagent cannot be employed for detecting brucin, as the former 

 gives the xanthroproteic acid reaction, and the latter the sugar-albumin 

 reaction. If, however, the section to be examined is first treated with 

 light petroleum to remove the fat, and a mixture of selenie and nitric 

 acids is afterwards added, the cell-walls assume a bright red colour 

 which gradually changes to orange, and then to yellow, whilst the 

 parts containing no brucin remain uncoloured. In order to detect 

 strychnin, the fat, grape-sugar, and brucin are removed by macera- 

 tion with light petroleum and with absolute alcohol, and then a solu- 

 tion of cerium sulphate in sulphuric acid is added ; this produces a 

 violet-blue coloration in the cell-walls, and afterwards a red coloration 

 inside the cells. 



Micro-chemical Examination of Minerals.! — If in a section a 

 mineral has been found which cannot be recognized by its optical 

 properties, morphological aspect, cleavage, &c.. Dr. A. Wichmann 

 recommends that the cover-glass should be removed, and the vfhole 

 slide together with the section smeared over with a thin fluid solution 

 of Canada balsam in ether by means of a soft brush. If it is not put on 

 too thickly, it is sufficiently dry in a few hours for further treatment. 

 The mineral to be examined is laid bare with a strong needle, or the 



* Zeitschr. f. Wiss. Mikr,, i. (1884) pp. 237-40. 

 t Ibid., pp. 417-9. 



