1110 
1) | Diffused SKL 190’ | 0.0635 0.01412 
Darkness 190’ Do 0.03925 
Diffused light 190’ Do 0.01414 
4 | Darkness 190’ Do 0.03925 
AN | Diffused light 190’ Do 0.01411 
| Darkness 190%. =| Do 0.03925 
Diffused light | 190’ | Do | 0.01411 
Z | Darkness | 190’ Do | 0.03925 
The following three experiments were carried out in an atmosphere 
of nitrogen. 
_ Diffused light | 190’ 0.0635 | 0.01416 
Dae 190 Do | 0.03928 
5 Diffused light 190’ Do | 0.01412 
Darkness | 190’ Do 0.03924 
. Diffused light | 190’ Do | 0.01411 
ae Darkness | 190’ Do | 0.03926 
The following three experiments were carried out in an atmosphere 
of carbon dioxide. 
| Diffused light 190’ 0.0635 | 0.01415 
ne | Darkness | 190’ Do 0.03928 
a Diffused light | 190’ | Do | 0.01411 
| Darkness 190’ | Do | 0.03928 
Diffused light | 190°, | Do | 0.01413 
=" Dannes 190 | Do | 0.03926 
Evidently the behaviour of this actinometer is quite regular. 
Potassium oxalate may be substituted for ammonium oxalate and 
the potassium oxalate-iodine actinometer works as well as the ammo- 
nium oxalate-iodine actinometer. 
Eper’s (Sitzungsber. der Kaiserlichen Akademie der Wissenschaften, 
Wien, October 1879) actinometer, which consists of a mixture of a 
saturated solution of ammonium oxalate and mercuric chloride, is 
generally used; but unfortunately there are several disadvantages of 
this actinometer. WiuntrHer (Zeit. Wiss. Photo (1909) I, 409) has 
shown that oxygen plays the part of a negative catalysor in the 
photo-catalysis of the reaction of a solution of mercuric chloride and 
ammonium oxalate in light. It is well-known that after exposure 
to sunlight Eper’s solution begins to separate mercurous chloride 
according to the following equation : 
