IV. Note on protagon

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In his communication to the Royal Society of January 6th last, on the subject of the presence or absence of potassium in protagon, Dr. Thudichum endeavours to raise an entirely false issue. The question I had to decide was not whether protagon contains a trace of potassium, but whether, to quote Dr. Thudichum’s own words, it con­tains “no less than 0·76 per cent, of potassium.” In the first instance I endeavoured to settle this matter by spectroscopic investigation, and employed two samples of protagon which had been prepared under Dr. Gamgee’s direction in the course of the research of which he com­municated the results to the Royal Society. In one of these samples, which had been four times crystallized, I was unable to detect any potassium; the quantity of the body at my disposal was however small, as the rest of the specimen had been employed in previous work, and Dr. Gamgee placed in my hands a large sample of protagon only twice crystallized, which had been prepared by Dr. Blankenhorn under his direction, and it was an analysis of this latter specimen which I communicated to the Royal Society. As stated, I estimated by spectroscopic means the amount of potassium present in 1 grm. of the substance to be 1/20 of a milligram, that is, 0·005 per cent. To these observations of mine, Dr. Thudichum replied by a paper entitled “On the Modifications of the Spectrum of Potassium which are effected by the presence of Phosphoric Acid, and on the Inorganic Bases and Sails which are found in combination with the Educts of the Brain.” In this paper an attempt is made to prove that remarkable difficulties exist in obtaining the characteristic potassium line, and when even pure potassium phosphate is strongly heated. I do not deem it necessary to discuss with Dr. Thudichum, as bearing upon the detection of potassium by the spectroscope, the accuracy of such a statement as the following:—“Even a large bead of pure potassium phosphate, when ignited before the slit of the spectroscope never produces even at a white heat any such intense red potassium line as the smallest bead of potassium chloride,” but shall merely state that, by numerous experiments, I have satisfied myself of the ease with which traces of potassium phosphate can be detected spectro­scopically even in presence of a large excess of phosphoric acid; and that I am convinced thatthe estimate of the quantity of potassium present in the protagon reported upon in my first communication was a remarkably close approximation to the amount really present.

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