538 J. 21. Blake — Picking Out and Mounting Diatoms. 



completes the adhesion of the two gelatine rings after the 

 monobromide has been included. After this sealing ring has 

 dried and has proved to be secure, and not till then, a final 

 ring of shellac is applied. Any other cement that will resist 

 the action of immersion fluids can be used in place of shellac. 

 A recent sample of bleached lac has developed fine cracks on 

 drying. The older slides did not show these cracks, in the 

 rings. The use of shellac is to protect the gelatine from damp. 



The gelatine preparatory rings were composed of gelatine 

 twenty grains, sugar ten grains, and water two and one-half 

 drams. These preliminary rings need not be thicker than the 

 height the diatoms makes necessaiw. Experience has shown 

 that these rings should be broad, and that the surfaces of 

 contact should be perfectly even. The final sealing gelatine 

 ring may be made of more concentrated gelatine, rendered as 

 thick by evaporation of a portion of the original preparation 

 as will flow easily from the brush. The flow will depend to a 

 great extent upon the temperature of the room. 



This gelatine seal can also be used for holding the solution 

 of phosphorus in carbon disulphide when this solution is 

 employed as a mounting medium. 



Westville, Conn. 



