Mr. Warington on the Green Teas of Commerce. 507 



spirits of wine, or japanners' gold size, are then to be placed 

 round the margin, so as completely to inclose the oil, and the 

 crystals are permanently preserved for observation. It may 

 be perhaps as well to observe, that the one layer of varnish 

 must be allowed to dry for about twenty-four hours before the 

 next is applied, and that during this time the slider must be 

 maintained in a flat position. 



LXXV. Observations on the Green Teas of Commerce. 

 By Robert Warington, Esq.* 



IN examining lately some samples of tea which had been 

 seized, from their being supposed to be spurious, my 

 attention was arrested by the varied tints which the sample 

 of green tea exhibited, extending from a dull olive to a bright 

 greenish blue colour. On submitting this to the scrutinizing 

 test of examination by the microscope with a magnifying 

 power of one hundred times linear, the object being illumi- 

 nated by reflected light, the cause of this variation of colour 

 was immediately rendered apparent, for it was found that the 

 curled leaves were entirely covered with a white powder ha- 

 ving in places a slightly glistening aspect, and these were 

 interspersed with small granules of a bright blue colour, and 

 others of an orange tint : in the folded and consequently more 

 protected parts of the curled leaves these were more distinctly 

 visible. By shaking the whole of the sample mechanically for 

 a short time a quantity of powder was detached, and from this 

 a number of the blue particles were picked out under a mag- 

 nifying glass, by means of the moistened point of a fine camel's 

 hair pencil. On being crushed in water between two plates 

 of glass they presented, when viewed by transmitted light, 

 a bright blue streak. This change in the method of illumi- 

 nating the object was necessary for the purpose of seeing the 

 action of the following tests: — A minute drop of a solution of 

 caustic potash was introduced by capillary attraction between 

 the glass plates, and the blue tint was immediately converted 

 to a dark bright brown, and the original blue colour again 

 restored by the introduction of a little dilute sulphuric acid. 

 It was therefore evident that these particles consisted of the fer- 

 rocyanide of iron or Prussian blue. The orange granules on 

 examination proved to be some vegetable colouring substance. 



To ascertain if possible the nature of the white powder ob- 

 served on this sample, I separated some of the dust, and 

 heated it to redness with free exposure to the air; the whole 

 of the vegetable matter and Prussian blue was thus destroyed, 



* Communicated by the Chemical Society ; having been read February 

 5, 1844. 



