240 ANNUAL OF SCIENTIFIC DISCOVERY. 



the action of the air; it is found that in five or six minutes a decided epoch 

 is attained from which to date the comparative action. In order to sec the 

 color, the liquid must be allowed to trickle down the sides of the vessel, and 

 collect itself at one point of the circumference at cither end of the cylindri- 

 cal part of the bottle. This part must be raised up to the level of the eye, so 

 that the longest axis may be presented to the sight, and thereby the deepest 

 shade of color. It requires some time to accustom one's self to the sight of 

 such a small amount of color; but when it is once well observed, it will be 

 found to be a method which will admit of the greatest precision. The first 

 few drops which are poured in will probably be decolorized at once; a few 

 drops more must then be added; if they become decolorized a few more must 

 bemused, and so on, until there is a perceptible amount of color remaining. 

 When this occurs the experiment is concluded. The amount of the reagent 

 used is then read off from the graduated measure. If the liquid be of proper 

 strength, and the bottle the required size, the number of grains gives the 

 comparative quantity at once. Sometimes the amount of organic matter is 

 so small that there is no appreciable action, or even the smallest amount of 

 solution by one A'esscl of air. In this case it is necessary to fill the bottle 

 several times. Some of the principal results obtained by this method were 

 as follow : 



Relative Quantities of Organic and other Oxidizable Matter in tJie Air of 



Manchester (average of 131 experiments) 52-9 



All Saints, E. wind (37 experiments) 52 4 



" " "W. wind, less smoky (33 experiments) 491 



" " E. wind, above 70 Fahr. ( 16 experiments) 58-4 



" " below, " (21 experiments). ... 480 



" In a house kept rather close 60 7 



In a pigstye uncovered 109-7 



Thames at City, no odor perceived after the warmest \veather of 1858. . 58-4 



Thames at Lambeth 43 2 



" AYaterloo Bridge 43-2 



London in warm weather (6 experiments) 29-2 



" after a thunderstorm 12-3 



In the fields S. of Manchester 13-7 



" N. of Highgate, wind from London 12-3 



Fields during warm weather in N. Italy 6'6 



Moist fields near Milan IS'l 



Open sea, calm (German Ocean, 60 miles from Yarmouth) 33 



Hospice of St. Bernard, in a fog 28 



N. Lancashire about same. 



Forest of Chamouni 2-8 



Lake Lucerne 1*4 



The first experiments undertaken were in Manchester, and the average 

 amount obtained was in the city about 50, gradually diminishing in moving 

 towards the country, until it was found in the fields at 13 ; on passing a sewer 

 stream about a mile from the outskirts, the amount ros.e to 83. The atmos- 

 phere on the Thames was not measured whilst at its worst, but immediately 

 afterwards; when, however, it had ceased to affect the senses of most persons 

 at least, the amount was very high, viz., 58. Moisture itself does not pro- 

 duce any action on the test ; one of the lowest numbers obtained was on the 

 German Ocean, about GO miles from land; the day was calm and clear. 

 The influence of height was very decided; in the higher grounds of Lanca- 

 shire, near Preston, the numbers being from 2 to 4. What is abundantly 



