36 Dr. H. E. Roscoe. Note on Protagon. [Mar. 31, 



Bases and Salts which are found in combination with the Bducts 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 spectro- 

 scopically 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. 



After Dr. Thudichum's reply, which seemed to leave it an open 

 question, whether any reliance should still be placed upon his state- 

 ment that protagon contained 0"76 per cent, of potassium, I deter- 

 mined to check that statement by a gravimetric analysis. Unfortu- 

 nately a sufficient quantity of the sample first analysed was not 

 available, and Dr. Gamgee supplied me with the remains of 130 grms. 

 of protagon, twice crystallized, which had been prepared under his 

 eye by Mr. Adolph Spiegel for experiments on the products of decom- 

 position of that body. It was this specimen in which an analysis 

 proved the presence of O0236 per cent, of potassium. So far, there- 

 fore, from confirming Dr. Thudichum's statement, this specimen was 

 found by me to contain less than one-thirtieth of the amount of potas- 

 sium which Dr. Thudichum asserts to be present in protagon. 



That the first crystallizations of a proximate principle of the brain, 

 such as protagon, should contain a trace of potash-salts is what would 

 naturally have been anticipated from a knowledge of the nature of 

 the soluble salts of the brain, and, therefore, to argue against the in- 

 dividuality of protagon, because of the presence of O0236 per cent, of 

 potassium in a second crystallization-product, appears to be entirely 

 fallacious. 



