52 Dr MoncJcman, Action of Copper Zinc Couple [Feb. 24, 



desiccator. I therefore next ground my sulphate of copper with 

 the following vehicles, painting each out on glass : 



(1) Boiled oil alone (best commercial), 



(2) Copal varnish alone, 



(3) Common rosin in turps, 



and two with amber varnish, one prepared by dissolving amber 

 in turps, the other by dissolving it in oil. These were placed 

 under a desiccator and left to dry. Some of them dried very 

 slowly, and had to be assisted by warmth till at last all were dry. 

 I then removed the sulphuric acid from the desiccator and replaced 

 it by water, thus leaving them in an atmosphere saturated with 

 moisture. Very soon some of them began to turn green, and 

 after a week all had turned green except one of those painted 

 with amber varnish. This experiment indicates, I think, the 

 following conclusions : 



(1) That neither boiled oil nor rosin varnish, nor copal varnish, 

 protect a pigment absolutely from moisture. 



(2) That amber varnish properly prepared does do so. The 

 amber varnish that protected the sulphate of copper was that 

 prepared with turps. The one prepared with oil failed to do so. 

 Therefore we may take it that Van Eyck probably used an amber 

 varnish. 



(2) On the Action of the Copper Zinc Couple on dilute solutions 

 of. Nitrates and Nitrites (NaHO and KHO being absent). By 

 James Monckman, D.Sc. Lond., Downing College, Cambridge. 



It is usually stated that when a dilute solution of a nitrate, 

 containing a copper zinc couple, is boiled for some time, the whole 

 of the nitrogen in the nitrate is given off as ammonia, which 

 may be used as a means of estimating the quantity of nitric 

 acid. When NaHO or KHO is added to the liquid good results 

 are obtained, but when no such addition is made the quantities 

 of ammonia found, by students working in the University 

 Laboratory, has fallen so far short of the true amount, that it 

 appeared to point to some other reaction taking place at the 

 same time. I was therefore asked to examine it carefully in 

 order to discover why the ammonia found was not equivalent 

 to the nitrate used and what became of the remainder. 



Quantities obtained from KN0 3 . My first endeavour was to 

 try what kind of results could be obtained by the method, how 

 far the various experiments could be made to agree in the 

 quantity of ammonia evolved and the amount of nitrogen that 

 disappeared. A very large number of experiments were per- 



