276 



CORRESPONDENCE. 



But I do not want chloroform, nor benzole, as suggested t>y 

 Captain Lang ; and I dispose the scales, not upon the cover, but upon 

 the slip of glass itself. 



As to the Canada balsam, I take great care to use that quantity 

 which will spread under the cover, and no more. 



Thence no washing or cleaning, which is always a very tedious if 

 not a very dangerous process. 



Your obedient servant, 



Chev". F. Huyttens de Terbeoq. 

 Brussels, Apnl 22, 1871. 



On Cells. 



To the Editor of the ' Monthly Microscopical Journul.^ 



Kochefort-sxjb-Meb, April 14, 1871. 

 Sib, — I read with interest in last December's number of your 

 excellent Journal a note on the method of selecting and mounting 

 Diatomacece, written by Captain Lang, President of the Reading Micro- 

 scopical Society. Certain cells made of gold size by Captain Haig, a 

 very skilful micrographer, are described in it. He states that cells of 

 gold size may be exposed to intense and prolonged heat, through the 

 action of which they become perfectly black and carbonized, while 

 the Canada balsam is unable to alter them. The process which he 

 describes for calcining such cells requires a great deal of time and 

 some trouble, and I see no need for its adoption. Excellent cells for 

 microscopical preparations may be made of Bitume de Judee (which is 

 natm-ally black), of asphalte, or of marine glue dissolved in spirit of 

 turpentine or in benzine. If the smoke, or rather the vapoui', dis- 

 engaged from gold size, already calcined, and heated again, is ajjt to 

 form crystals, much more strongly must this effect take place when 

 bitumen, not previously heated to excess, is used. In order to remedy 

 this inconvenience, I have been accustomed to prepare beforehand a 

 number of cells, and so to have always at hand some dozens of slides 

 ready for use ; but at the moment of using them I do not expose them 

 to heat. Formerly, in order to make the cover adhere, I used to apply 

 ■& second layer of varnish over the first. This sometimes caused an 

 inconvenience more serious than the one already pointed out. The 

 new bitumen spread itself gradually into the preparation, and at last 

 altered it completely. There is a very simple means of avoiding this 

 danger, and I will now describe it. A circle of bitumen, about one- 

 third smaller than the covering glass, is drawn beforehand on my 

 slides. When I wish to make a preparation, instead of coating, as 

 formerly, the first circle with a second layer of bitumen, I form a 

 second circle of it outside the first, and as near as possible to it, and 

 each of the two circles has its own advantage ; the fii'st, in fact, while 

 forming the cell, serves as a support for the covering glass, and thus 

 preserves the Diatomacete from any breakage ; it ofiers besides a serious 

 obstacle to the spreading of the more liquid bitumen of which the out- 

 side circle is composed, and the latter closes the cell by fixing the cover, 



