The subject of these investigations, some of the results of which are before the Society to-night, was suggested to me by Professor Carl Ludwig, and was carried out in his laboratory at Leipzig, where I worked with the help of his assistant, Dr Drechsel, to whose kindness and large knowledge of the subject I was much indebted.

In this paper I shall give simply an account of the method of analysis, leaving for the future a record of the facts which it has enabled me to obtain.