MR. W. CROOKES OK REPULSION RESULTING FROM RADIATION. 251 
Brown powders therefore act most like black. The low action of bismuth peroxide is 
probably due to its pale brown colour, which acts therefore like a mixture of brown 
and white. It will be understood that in classifying all varieties of coloured bodies 
under a few headings, great differences in intensity and tint must be associated 
together in the same Table; 
228; Table V. — Yelloiv Powders. 
No screen. 
Water screen 
interposed (5 millims.). 
Lampblack ( standard disk) 
. . 100-0 
100-0 
Tungstic acid (hydrated) 
. . 57-9 
26-9 
Tungstic acid (anhydrous) 
. ' . 50-8 
72-2 
Persulpho-cyanogen 
. . 43-9 
ii-5 
Ceroso- ceric oxide 
. . 38-7 
141 
Uranic oxide 
. . 33-8 
11 : 8 
Cadmium sulphide . . .... 
: . 32-6 
10-6 
Milk of sulphur. ........ 
. . 30-5 
7-7 
Sulphur, precipitated 
. . 25-6 
19-8 
Antimonic acid 
. . 22 ; 6 
8-1 
The averages of the two columns are, without a water screen, 37'4, and with a 
water screen, 20'3. But anhydrous tungstic acid behind water is so different from the 
others that a fairer mean will be- obtained by omitting this powder. The figures 
now become 357 and 13‘8. 
229. Table Vi. — Green Powders. 
No screen. 
Water screen 
interposed (5 millims.). 
Lampblack ( standard disk) ....... lOO'O 
Green salt of Magnus (diammonio-platinous 
chloride) :..... 89 ; 5 
Chromic oxide, pale green 71 ; 5 
,, bright green ...... 63'4 
100-0 
103-5 
20-2 
4S ; 8 
These are too few in number to make it safe to draw any inference from the results. 
The great difference in action behind a water screen caused by a little change in 
colour of chromic oxide is worth notice, and will be again referred to. 
230. Table YII. — Blue Powders. 
No screen. 
Water screen 
interposed (5 millims.). 
Lampblack ( standard disk) 
. . 100-0 
ioo-o 
Tungstic oxide 
. . 91-3 
100-1 
Copper carbonate 
56-5 
„ phosphate 
. . 52-0 
52T 
„ tungstate 
. . 51-2 
77-0 
„ oxalate 
. . 30 T 
40-2 
2 k 2 
