solution of potassium bromide, first in the cold, then by heating. The potassium bromide had been made thus: Twice recrystallized potassium hydrogen tartrate was heated in a platinum dish in a muffle furnace until it was converted into carbonate, and the excess of carbon burned off. It was then dissolved in water, filtered and neutralized with some of the hydrobromic acid already described. The carbonate had been tested for both sulphuric acid and chlorine with negative results. After the silver bromide had been digested with the potassium bromide, it was washed very thoroughly, suspended in water, and a current of hydrogen sulphide passed into it. This converts it into sulphide hydrobromic acid being liberated. The acid was drained off on a porcelain plate, and then distilled a number of times. It was finally tested and found to be perfectly free from sulphates and also did not contain free bromine. Having started with an acid which was probably pure and subjected it to these operations with reagents free from chlorine, there can be no doubt as to the purity of the resulting acid. The hydrogen sulphide used was prepared from potassium hydrosulphide as in the sulphide method, and washed first with a solution of the hydrosulphide, then very thoroughly with pure water. From the hydrobromic acid obtained, a specimen of cadmium bromide was prepared as before and sublimed twice in a vacuum. This specimen was used for determinations IV and V. Method of Analysis. The first three determinations were made exactly like those in the chloride method. The last two were also made in the same manner, only the washing of the precipitate was varied. After the silver bromide had been contracted by warming on a water-bath it was washed by decantation and then agitated violently with cold water to remove occluded nitrates, but it was then so finely divided that it could not be filtered. The artifice used by Stas to contract it a second time was to pass a current of steam into the milky liquid. This was tried here, but for some reason or other did not work very well, and considerable difficulty was had in filtering it. The results of the five determinations are tabulated below. All weighings are reduced to the vacuum standard on the basis of Sp. Gr. of CdBr_{2} = 4.6 and Sp. Gr. AgBr = 6.62.