188 DR. R. ANGUS SMITH 



by the ^eatest refinement, were used as scientific instru- 

 ments by Pettenkofer. 



It is not pleasant to speak of the history of discoveries,, 

 as we so often find tbat much that is discovered is so for 

 the second time and not for the first ; but it is extremely 

 improbable that Pettenkofer knew of Hadfield, and it is 

 very probable that Hadfield, whom I long knew, could not 

 have carried out the refined experiments of Pettenkofer. 

 Besides, the use made of the instrument by the Munich 

 professor is more important than the instrument itself. 



It was one of my duties, in connexion with the Royal 

 Mines Commission, to examine into the subject of tests, in 

 order to find a simple method of determining the value of 

 the air in mines. I saw clearly that my test for oxidizable 

 matter was valueless in such places, and Pettenkofer^s could 

 not be used comfortably, or at least would not be used. 

 More simplicity was required. There must be little to 

 carry, little to do, and little to think of. Nothing better 

 than baryta or lime suggested itself. The comparison of 

 precipitates of lime, as Dr. Boswell Reid recommended, 

 failed long ago, because the precipitates changed in physical 

 appearance; but his mode of keeping the extent of the pre- 

 cipitate in the memory did not exactly fail, and was to be 

 considered correct or otherwise, according to the memory, 

 and according to the frequency of the experiment. 



Equal quantities of baryta-water were poured into two 

 bottles; air was blown into them from the lungs until 

 a decided precipitate formed, equal in both cases. The 

 amount of precipitate was estimated by testing the amount 

 of baryta still in solution. When this was done several 

 times by two persons, the results were almost absolutely 

 the same. Next day, these same two performed the ex- 

 periment, relying on the memory of the precipitate of the 

 previous day ; and the results were that the oxalic acid 

 required was 23-7 cub. centims., 23*2, and 23"2. The 



