324 Mr Stevenson Macadam on the 



a great many of the failures to find iodine are to be attributed 

 to this — and that not only in the analyses of plants, but also in 

 testing for iodine in cod and skate liver oils, where the practice 

 has been to add caustic potassa and incinerate at a high tem- 

 perature. In such cases, notwithstanding that the oil probably con- 

 tained iodine, and that it was certainly present in the potassa, yet, 

 after examination, it has not been detected in the ashes. To avoid 

 the loss of iodino thus sustained, Ohatin recommends the addition 

 of potassa to the plant previous to incineration.* But this, whilst 

 it will no doubt, to a certain extent, hinder the volatilisation of 

 iodine, will not ensure its retention ; and moreover, the saturation 

 of the plant with ordinary potashes, necessarily causes the addition 

 of the very element that the experimenter is in search of. The only 

 safeguard which I have adopted is to burn the plant in a chamber 

 with a small quantity of air, and where there is little draft. In this 

 process it can hardly be said that the plants are burned — the term 

 should rather be that they are charred. They are then finely 

 powdered, digested in hot water, and filtered ; the clear liquid is 

 evaporated to dryness and subsequently treated like the potashes. 



In the following list of plants there are representatives from differ- 

 ent districts and from different altitudes. In the majority of cases 

 a large quantity of the plant was used in the examination, and so far 

 as could be inferred from the depth of the rose or blue tint assumed 

 by starch, the quantity of iodine in different plants was very 

 various. But as no attention was paid to the weight of the original 

 bundles of dried plants, or even to that of their ashes, I would re- 

 frain from speculating as to any law which might regulate the in- 

 crease or decrease of iodine in plants belonging to different natural 

 orders, or grown in dissimilar situations. Moreover, there are a 

 number of plants in which I have failed to detect iodine; and whilst 

 it is probable that some or most of thern may be destitute of that 

 ingredient, yet, considering the many ways in which so volatile a 

 substance could have escaped, I propose to make other trials with 

 those negative plants, before I announce their names, and the locali- 

 ties from which I received the specimens worked upon. 



As having some connection with the subject treated of, I would 

 intimate that I have obtained distinct indications of the presence of 

 bromine in crude potashes. It is unfortunate that our tests for 

 bromine are so much inferior in delicacy to those for iodine, that it is 

 necessary to operate upon very large quantities before the indica- 

 tions of the former element are distinct. There is no doubt that, from 

 the presence of bromine in trees, it will be found in greater abun- 

 dance in the more succulent plants ; but tho {aw trials I have yet 

 made have been unsuccessful in determining its presence in any but 

 the crude Canadian and American potashes. 



Comptea RenduS; tomo xxx., p 354 



