[ 264 ] 



^ecbnolog^ of Biatoms,* 



By J. Tempere. 



Chapter III.-ON THE MOUNTING OF DIATOMS. 



DIATOMS prepared as I have described in the preceding 

 chapters are mounted in two ways — either dry or in a 

 medium. These two methods apply equally well to mixed 

 Diatoms — that is to say, to washings spread out on a thin plate — 

 as to species that are sorted and isolated. 



The Dry Method. 



The mounting of Diatoms dry is the less used of the two 

 methods ; it requires more care and more attention than when a 

 liquid is used, for it is necessary to exclude all trace of moisture in 

 the cell and also to prevent its subsequent introduction. 



Preparation of the Cells. — The cells should be made of a 

 cement of black gum-lac, prepared as follows : — In a vessel of tin 

 (a sardine-tin will do very well) you heap up white gum-lac to half 

 its depth, and having made a saturated solution of aniline black 

 in alcohol of 90^ (absolute alcohol), pour enough of it over the 

 gum to cover it ; allow them to remain in contact for a few 

 minutes, and then place the tin in a water-bath, stirring the 

 mixture till the lac is completely dissolved ; then, while warm, pass 

 the mixture through muslin. In cooling, this cement becomes 

 semi-liquid, and has just the consistence which it ought to have to 

 meet the requirements of the operation. When, in consequence 

 of the evaporation of the alcohol, it becomes too thick, a few 

 drops of absolute alcohol may be added, taking care that it is 

 well stirred up. 



The cells — which ought to be made on the turn-table — should 

 have always the same exterior diameter as the thin glass which is 

 to cover them ; their thickness may vary from the i/8th to the 

 i/ioth of a millimetre. One good coat of cement is generally 

 enough. 



In order to make a good cell — that is to say, one that is not 

 too large and of even thickness throughout — it is well to use a 

 sable brush of the best quality, of which the hairs are not more 

 * Translated from Le Diatomiste. 



