EXPERIMENT. 37 



any 'known means ; but it seems almost certain that some 

 series of elements, for instance Iodine, Bromine, and Chlo- 

 rine, are really compounds of a simpler substance. We 

 must doubtless look to the production of intensely high 

 temperatures, as yet quite beyond our means, for the de- 

 composition of these so-called elements. But it may very 

 possibly be found that, in this age and part of the uni- 

 verse, the dissipation of energy has so far proceeded that 

 there are no sources of heat left to us sufficiently intense 

 to effect the decomposition of the supposed elements. 



Interference of Unsuspected Conditions. 



It may often happen that we are not aware of all the 

 conditions under which our researches are made. Some 

 substance may be present or some power may be in action, 

 which escapes the most vigilant examination. Not being 

 aware of its existence, we are of course unable to take 

 proper measures to exclude it, and thus determine the 

 share which it may have in the results of our experiments. 

 There can be little doubt that the alchemists were often 

 misled and encouraged in their vain attempts by the un- 

 suspected presence of traces of gold and silver in the 

 substances they proposed to transmute. Lead, as drawn 

 from the smelting furnace, almost always contains some 

 silver, and gold is associated with many other metals. 

 Thus small quantities of noble metal would often appear 

 as the result of experiment and raise delusive hopes. 



In more than one case the unsuspected presence of 

 common salt in the air has caused great trouble. In 

 the early experiments on electrolysis it was founpl that, 

 when water was decomposed, an acid and an alkali were 

 produced at the poles, together with oxygen and hy- 

 drogen. In the absence of any other explanation for this 

 singular result, some chemists rushed to the conclusion 



