1910-11.] Absorption of Light by Inorganic Salts. No. I. 525 
The figures for the iodide are the mean of two independent determina- 
tions, for the chloride the mean of four independent determinations, and for 
the others the mean of three independent determinations, taken in the 
same way as for the case of the nitrate. The value of c gives the concen- 
tration of the solution for which the determination was made, in gramme- 
molecules per litre. The thickness of the cell used is given by d. 
When the chloride, bromide, and particularly the iodide solutions were 
left standing some time a slight precipitate formed, which in the case of 
the first two salts was yellowish, and in the case of the iodide was chocolate- 
coloured. It sometimes made the solutions slightly turbid, and caused a 
noticeable increase in the value for A for those points for which it is small. 
On filtering the solution, however, A always dropped to its former low 
value. The solution of the fluoride used was a saturated one. The effective 
width of the thermopile was - 4 mm., the width of the slit was "3 mm., except 
for the first two points, for which it was 1*0 mm. With a thickness of 
solution equal to 1 cm. it is not possible to go further into the infra-red 
owing to the absorption of the water itself. 
