Manchester Memoirs, Vol. xlvii. (1903), No. 15. 7 



all deposited at this point in the different tubes (where 

 the cold water comes in contact with the glass), more 

 accurate measures of. the quantities of the deposits are 

 obtained. 



With the view of keeping the tubes hot to the point 

 at which the cold water comes in contact with the narrow 

 glass tube, to prevent the formation of a mirror before 

 the portion of the tube is reached on which it should be 

 deposited, I put a small coil of copper or platinum gauze 

 I of an inch square around the tube, so as to cover the 

 rounded part of the drawn-out portion and part of the 

 narrow tube to within i^ mm. of the paper. I use a flat 

 Bunsen flame one inch wide, the flame acting on about 

 f of an inch of the uncovered glass tube, with the end of 

 the flame playing on the wire gauze. 



Fig. 4 shows mirrors obtained by the cooling 

 process on the tubes of accurately measured internal 

 diameter. 



The apparatus employed for carrying out the process 

 is shown in Fi^. i. 



Fading of the arsenic mirrors and black deposits. 



In my previous papers on the approximate estimation 

 of arsenic, I have mentioned that I had not observed that 

 any of my arsenic mirrors had faded even when exposed 

 to air and light, but, as other chemists had had experience 

 of fading, and had recommended the sealing of the mirrors 

 in an atmosphere of hydrogen to prevent it, I considered 

 it desirable to carry out this process, and have since 

 done so. 



I was much surprised, however, to find that the mirrors 

 which were made by the old process, and the original 

 photographs of which are seen in Fig. 5, faded after 



