94 Dr. R. D. Thomson on the Mode of Testing Alcoluol. 



proportion of water in each of the foregoing specimens — inside, outside, 

 and in the whole slice : — 



Inside. Outside. Whole Slice. 



1 74-5 699 72-2 sound. 



2 76-2 73-3 74-8 diseased. 



3 79-3 750 777 sound. 



4 76-2 74-8 75*6 diseased. 



5 782 75-1 76-9 sound. 



6 779 73-2 759 do. 



7 81-8 761 78-6 diseased. 



8 76-5 71-6 74-6 sound. 



9 82-6 77-6 80-5 do. 



10 772 720 74-9 do. 



11 791 74-7 773 do. 



12 810 76-2 78-8 do. 



Average, 78-6 74*2 76-6 



If a potato be grated down, and the juice squeezed and washed out of 

 the pulp, the latter has no tendency to change colour by exposure to the 

 air. The juice also, if bottled up, as soon as it is expressed, retains its 

 yellow colour unchanged, letting fall after some time, a deposit of the 

 same colour. But if the juice be freely exposed to the air it soon be- 

 comes brown, and deposits a blackish powder, which by washing and fil- 

 tering, may easily be obtained in a separate state. It consists partly of 

 the woody matter of the cells, and partly of a black extractive matter, 

 which is known as a frequent result of the decay of plants. It is this 

 substance, entangled among the cells and farinaceous matter which occa- 

 sions the brown colour peculiar to the naturally diseased potato. 



XVI. Mode of Testing Minute Quantities of Alcohol. 

 By Robert D. Thomson, M.D. 



The determination of the presence of minute quanties of alcohol, is a 

 chemical point of some importance, especially in judicial cases. The 

 usual method hitherto adopted for detecting alcohol in mixed fluids, is to 

 subject the fluid suspected to contain it to distillation, at a temperature 

 not greater than that which is required to cause the alcohol to pass over 

 into a receiver, and then to judge of the presence of spirit by the vinous 

 odour of the distilled fluid. When alcohol in the form of gin, whisky, 

 or brandy, &c, has been swallowed, if death takes place within a short 

 period of the introduction of the fluid, the odour of the spiritous liquors 

 will be distinctly perceptible to one inspecting the interior of the stomach ; 

 but if a considerable time should elapse, as, for example, a few hours 



