PARIS -GREEN. 79 



several grounds. If one mixes soft-soap direct (and in weak solution 

 with water) with Paris-green, you get a decidedly alkaline mixture, and 

 the circumstances thereby induced which would tend to cause the 

 copper (as explained in my last note) to be partly thrown down. It 

 might not happen in a weak solution, but would be much more likely 

 to do so if soap and Paris-green were directly mixed. 



" The remark in your letter as to the change of colour you noticed 

 in the outside portion makes me think that partial reduction has 

 actually taken place, and if so, that means a change of composition. 

 I have to-day made such a mixture, and will keep it to see what 

 happens. 



"But there is yet another great objection: the soft-soap may 

 simply be a cheap medium for ' wrapping up ' in it a little Paris-green, 

 and making it look a lot. If the purchaser wants such a mixture he 

 had better get the separate materials himself and mix them ; then he 

 may have a fair chance of getting the right amount of ' green,' other- 

 wise he will not. 



" Lastly, the mixture is a difficult one to mix up in water, at least 

 in cold water. I would certainly advocate the ' unmixed ' material for 

 purchase." — A. J. V. 



The above-mentioned experiment Dr. Voelcker carried out, and on 

 April 28th further wrote : — " I have now kept the mixture of Paris- 

 green and soft-soap, which I made for some time, and have compared 

 it with the tin of the similar compound which you sent me. 



" The appearance which the two present are identical. 



" As I said to you before, there is a change to a certain extent in 

 the composition, which is indicated by the darkening of colour noticed 



by you, and called by you the olive-greenish colour." Dr. 



Voelcker made some observations here in reply to remarks on various 

 colouring which I had noted, and then proceeded : — " That there has 

 been a change is quite enough to make the application of the term 

 * Paris-green ' not altogether a proper one, for it is no longer the aceto- 

 arsenite of copper. Whether, however, its properties are destroyed or 

 not is another matter, and, seeing that the evidence we have so far 

 goes to show that any salt of copper acts as a preventive against 

 mildew, one cannot say that the mixture has produced a body no longer 

 possessing the virtues of the copper compound." .... " The mixture 

 of soft-soap does not remove the copper, nor yet the arsenic ; they 



both remain there." After some further observations. Dr. 



Voelcker added : — " And again I call the mixture a very bad one for 

 mixing up with water ; it is a sticky, pasty mass that wants a lot of 

 rubbing about ; ordinary stirring in water does not do. It would be 

 much better to stir the pure Paris-green up in a soft-soap solution. I 



