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The Rev. Father Thompson's High Refractive Medium. 



Mr. E. M. ISTelson writes that it will be in the recollection of 

 some of the Members that a few years back he exhibited a 

 beautiful slide of diatoms, mounted in a very dense medium by 

 the Rev. Father Thompson. He is now, through the kindness 

 of Father Thompson, able to communicate the recipe of the 

 composition to the Club. He still has the same slide in his 

 possession, and,. so far as it is possible to judge, it has remained 

 unaltered. He therefore begs to commend Father Thompson's 

 high refractive medium to the especial notice of the Club as 

 the best thing that has been done in that direction. 



" Take flower of sulpMir, hromine^ and arsenious acid in the 

 proportions of 8, 10, and 12 respectively by weight. Dissolve the 

 sulphur in the bromine with gentle heat in a thinnish test tube 

 about six inches long. Over a small Bunsen jet add small 

 portions of the arsenious acid, boil and let the condensed 

 vapours of the mixture cool and fall down the sides again. Be 

 very careful that these do not escape. If none of these have 

 escaped, the proportions given will be correct, but, if they do 

 escape, probably a spot more bromine will have to be added to 

 keep the mixture clear. 



No mechanical directions can be given beyond these. Success 

 •is very much like that of a cook in his preparations, and the 

 eye and understanding must regulate the proceedings. When 

 made the mixture should be about the consistency of toffee and 

 much the same in appearance. It should be handled with a 

 piece of platinum wire. The more arsenic the better, and a 

 grain or two of the metal itself may be coaxed in towards the 

 end 'SO long as the mixture remains clear. If properly made 

 this will last, so far as I know, for ever." 



