by the contact of a Hydrogen-flame with various Bodies. 327 



In subsequent experiments care was taken to avoid the use of 

 any vulcanized india-rubber tubing. This destroyed the blue 

 seen on water and ice, but did not affect the other results 

 which have been enumerated. 



The sudden appearance of a blue colour when a hydrogen- 

 flame is brought into contact with a body, thus becomes a test 

 for the presence of sulphur, and as such it is one of great deli- 

 cacy. For example, after the fingers had touched a piece of vul- 

 canized india-rubber, the passage of them through a small quan- 

 tity of water caused the blueness to be seen on its surface. What 

 weight of matter was here employed in the production of a dis- 

 tinct colour I will not venture to suggest. The best mode of 

 observing the blue coloration on water, and indeed elsewhere, is 

 to bring the flame vertically down on to the surface of the 

 body examined : when a certain part of the flame reaches the 

 body, if sulphur be present, a blue ring of light is seen. 



I have to thank my friend Mr. Broughton for enabling me 

 to compare the delicacy of this physical test with the best che- 

 mical tests for sulphur. To accomplish this, milk of sulphur 

 was mixed with precipitated silica in varying proportions until a 

 point was reached at which the chemical reagent (nitroprusside 

 of sodium) failed to indicate the presence of sulphur. With 

 the hydrogen- flame, the silica alone gave no blue colour, but it 

 immediately appeared on the admixture of sulphur, and could 

 easily be recognized, not only in part of the very mixture where 

 the chemical test failed, but far beyond this degree. It is almost 

 needless to state that whatever was employed to support the 

 powder was carefully examined by the flame just before the 

 experiment was made. A mixture of silica and sulphur was 

 made containing the ^jth of a grain of the latter. Of this, 

 the minutest quantity that could be removed, less than -xJoth 

 of a grain, was placed on a piece of platinum or thrown on the 

 surface of water ; in either case, when contact with the hydrogen- 

 flame was made, the blue colour shone for a moment. By the 

 chemical test, the sulphur in a less minute quantity of the powder 

 remained undetected. If it could be uniformly mingled, I have 

 reason to believe that certainly the 100,000th part of a grain 

 of sulphur could readily be detected by means of the hydrogen- 

 flame. The presence of sulphur in the homoeopathic powders 

 which are said to contain a trace of that substance was easily 

 verified by moistening the powder (so as to prevent the com- 

 bustion of the sugar of milk) before it was examined by the hy- 

 drogen-flame : as the water evaporated, the blue was seen for an 



vulcanized india-rubber tubing was sufficient to raise its absorption several 

 degrees,* solely from the impalpable dust removed from the tubing. 



