26 



Dr. C. A. MacMunn. Researches into the 



the power o£ absorbing the ultra-violet rays cf the spectrum, though 

 they are inferior in this respect to benzene and its derivatives. 



2. Terpenes, with composition C 15 H 24 , have a greatly increased 

 absorptive power. 



3. Neither the terpenes themselves nor their oxides nor hydrates, 

 exhibit absorption bands under any circumstances when pure, but 

 always transmit continuous spectra. 



4. Isomeric terpenes transmit spectra which generally differ from 

 one another in length, or show variations on dilution. 



5. The process of diluting with alcohol enables the presence of 

 bodies of the aromatic series to be detected in essential oils ; and even 

 in some cases the amount of these substances present may be approxi- 

 mately determined. 



Researches into the Colouring-matters of Human Urine, with 

 an Account of the Separation of Urobilin." By Chas. A. 

 MacMunn, B.A., M.D. Communicated by A. Gamgee, 

 M.D., F.R.S., Brackenbury Professor of Practical Physio- 

 logy and Histology in Owens College, Manchester. Re- 

 ceived March 6, 1880. Read March 18, 1880. 



I do not propose to discuss in this paper all the pigments which 

 have been said to occur in urine, as their consideration would extend 

 over a considerable space ; and I shall, therefore, limit my observa- 

 tions to those which I have myself studied, and which are discoverable 

 by means of spectroscopic observation. Notwithstanding the efforts 

 of physiological chemists, at home and abroad, no one has been 

 hitherto able to isolate the pigment known as urobilin. After many 

 unsuccessful attempts, I have at length succeeded in isolating a 

 pigment, which, on account of its spectroscopic and chemical re- 

 actions, appears to be urobilin in a pure state. 



Although it has not been obtained in sufficient quantity to allow 

 of a formula being assigned to it, I believe that I shall soon be able to' 

 obtain enough for this purpose. A preliminary examination has 

 shown that it contains carbon, hydrogen, oxygen, and nitrogen. 



Preliminary Remarks. — If nitric acid be added to a solution of bile 

 before the slit of the spectroscope, the solution at once undergoes 

 a change of colour, becoming green, blue, violet, red, and, lastly, 

 yellow or brownish-yellow, and the spectrum is characterised by 

 having two bands : a broad shadowy band, composed of two in 

 orange and yellow, and a black band at Fraunhofer's line P. In a 

 short time the shading in orange and yellow begins to fade, and at the 

 time the oxidation process is completed, and the colour of the solution 



