364 A BLOWPIPE REAGENT—BOWMAN. 
on the tablet at a distance from the assay varying with their vola- 
tility. The potassic iodide solution I keep in a dropping bottle 
similarly to nitrate of cobalt. Acids are always present in a 
complete blowpipe cabinet. The keeping properties of the potas- 
sic iodide solution are proved by the fact that the solution now 
in the bottle, and with which some of the tablets before you 
were prepared, has been there since February, 1887, and still does 
its work perfectly. 
When I came to renew these experiments in preparing this 
paper it occurred to me that it would be a great improvement if 
I could produce the same results with the dry crystals of Potas- 
sic Iodide. As this reagent will only produce the proper results 
in the presence of an acid it was necessary to find a dry acid to 
be used with it. As sulphuric acid appears to be the best to use 
with the solution of potassic iodide, it seemed best to try a crystal- 
line sulphate. Copper and zine sulphates would not do, as each 
of these metals gives a characteristic coating with Potassic 
Iodide. I therefore tried common sulphate of iron, green vitriol, 
and found that the best method was to powder both crystals and 
mix the powders well before adding to the assay. By this 
means the method becomes as simple and convenient as the use 
of carbonate of soda or any of the fluxes ordinarily in use in 
blowpipe work. Thus we have distinctive tests by a thoroughly 
practical method for some metals and a second or check on the 
ordinary tests for others. If one wishes to take a blowpipe out- 
fit, for determining minerals, on a tour in the country, it is a 
great advantage not to have to carry acids. With regard to the 
plaster tablets, Dr. Haanel states that when blacked in a gas 
flame they are equal if not superior to charcoal for oxide coat- 
ings. If so, and if they can be made to take the place of char- 
coal for ordinary field work, it is an immense advantage, as they 
are easily prepared, clean to handle and occupy little space. I 
adopted Dr. Haanel’s method of making them, which is to spread 
a coating of plaster of Paris about } inch thick on a sheet of 
glass and just before it hardens to mark out the tablets with cuts 
nearly through to the glass. When dry they readily break 
apart. This method with dry potassic iodide has added seven 
