for the Preparation of Tin Tetrethyl. 



43 



These results indicate that, with the quantity of alloy used 

 (viz. 45 grins.), about 50 per cent, of the tin is always con- 

 verted into tin tetrethyl, no matter what the composition of 

 the alloy may be, so long as the proportion of tin does not exceed 

 from 20 to 60 per cent. They also show that the total quan- 

 tity of tin tetrethyl obtained is proportional to the percentage 

 of tin in the alloy up to about 33'3 per cent., but not beyond ; 

 possibly for the following reason: — A couple composed of tin 

 and copper only has no immediate action on ethyl iodide ; but 

 a zinc-copper couple is very active, giving zinc ethiodide 

 almost immediately. The production of this substance appears 

 to be a necessary preliminary to the formation of tin tetrethyl; 

 and therefore as the percentage of zinc is reduced, the forma- 

 tion of the zinc ethiodide is retarded, if not interfered with 

 altogether. 



Up to a certain point, then, sufficient zinc ethiodide is 

 formed to induce the reaction ; but if the percentage is further 

 increased, the action seems to stop, or at least to be hindered. 

 The following table illustrates this point. In each experiment 

 60 grins, of ethyl iodide was allowed to act on 50 grms. of 

 couple. 



Experiment. 



1. 

 2. 



3. 

 4. 

 5. 

 6. 

 7. 

 8. 



Percentage of Tin 

 in alloy. 



5 



10 

 15 

 20 

 33-3 



50 



Eeaction finished, 

 after commence- 

 ment*, in 



10 minutes. 



20 



30 



40 



30 



40 

 240 

 480 1 



1 In experiment 8 the digestion was stopped at the end of eight hours, 

 although the reaction was by no means finished ; for on distillation 24 grms. of 

 unacted-on ethyl iodide were recovered. 



From experiments 7 and 8, it is evident that the time 

 necessary for the action increases enormously with high per- 

 centages of tin in the alloy.' 



* The commencement of the action of ethyl iodide on the couple is 

 always indicated by an apparent effervescence in place of the simple ebul- 

 lition which occurs at first. 



