THE MICROSCOPE. 191 



[Translated from the " Journal de Micrographie," September No. for 1882.] 



PREPARATION OF DIATOMS. 



BY J. BRUN, PROFESSOR AT THE UNIVERSITY OF GENEVA. 

 Translated by P. R. B. de Pont, Instructor in French, University of Michigan. 



HERE is a new process I have devised to destroy the endochrom 

 of diatoms and thus permit to make preparations of them. It 

 is so convenient and gives such good results that I consider it a 

 duty to indicate it in a few lines. 



If we have a fresh magma of diatoms still moist, we must add 

 a few crystals oi permanganate of potassium and very little water — 

 about one part of the salt to ten of water. If the diatoms are dried 

 up, pure or mixed with earth or organic matter, we must moisten 

 them with a concentrated solution of the same salt containing a 

 few crystals in excess. 



The reaction of the permanganate must last about 12 hours. 

 It is well to stir now and then the mixture placed in a vial of an 

 average capacity of 100 gram., and to place it in a water bath or 

 expose it to the sun. 



Next the vial must be half filled with water and a small quan- 

 tity of calcined fnagnesia, about 0.50 centigr., added to it, which must 

 be left to act for two or three hours, giving it an occasional shak- 

 ing. Then we pour in a small quantity of not more than onegramme 

 and every ten minutes some pure chloric acid. 



When the whole contents of this vial have lost every trace of 

 color, the operation is ended. If need be, the reaction may be 

 facilitated by plunging the vial in water very hot or even boiling. 



Then we proceed with the usual washings and decantations, 

 and here let us remember that the absolute purity of the distilled 

 water, for the latter washings, stands always as an essential condi- 

 tion of success. 



In this process we have first the powerful oxydation of the endo- 

 chrom by the permanganate and the magnesia; then by means of 

 the acid, we obtain a liberation of gaseous oxygen which acts as- 

 oxydizing agent, and then of chlorine which acts as decolorant. It is 

 doubtless to these multiple and successive reactions on the outside 

 and even inside of the valves, that this most perfect cleaning of 

 their silicle must be attributed. By this treatment the delicate 

 species are not corroded, especially if, before the acid action, enough 

 water is added. The surface of the valves has lost all its coleoderm; 

 it appears in all its brightness and the minutest details, striae and 

 dottings are clearly brought out. 



I have tried successively, for the last years, all the various 

 physical or chemical processes that have been announced, and I can 

 say that I have found none which would succeed as completely and 

 regularly as the above. 



