JUNE 14, 1912] 
Irregular. 
Irregular indicates that at times the bird may 
be Common and at other times Rare. Often 
this has to be used in connection with one of 
the other seven terms. In such cases it is 
often necessary to add Usually; as: Cross- 
bill, Irregular, Usually Rare. 
Of course it is not intended that these terms 
should always be used by themselves. One 
may use them, when necessary, in conjunction 
with other words; as, Common Migrant, 
Searce Resident, ete. 
JOHN Drypen Kuser 
BERNARDSVILLE, N. J. 
TRIVALENT PLATINUM 
THE first evidences of the existence of com- 
pounds in which platinum acts with a valence 
of three were found about two years ago by 
Wohler. On carefully chlorinating PtCl, or 
dechlorinating PtCl, at 390°, a greenish-black 
powder was formed which had the formula 
PtCl,. This dissolved slightly in cold water, 
but more rapidly in hot, with the formation of 
an acid, H,PtCl,O, some hydrolysis also taking 
place. By precipitating with soda, a pure 
hydrated sesquioxid was obtained, but this 
could not be dehydrated without decomposi- 
tion. When the hydrate was dissolved in 
acid a mixture of chloroplatinous and chloro- 
platinie acids was formed. Wohler found, 
however, that when a dilute solution of cesium 
and a mixture of chloroplatinous and chloro- 
rin water, a dark-green powder is precipitated, 
of the composition Cs,PtCl,, which has a 
strong tendency to decompose into the chloro- 
platinite and chloroplatinate. 
This work has been strikingly confirmed in a 
paper read by Levy before the Chemical Society 
(London) on March 25. Levy was working 
on the copper-red iridescent salt, discovered by 
Hadow, which is formed when chlorin or 
bromin is added to a solution of potassium 
cyanoplatinite. To this Hadow gave the 
composition of 5K,Pt(CN), - K,Pt(CN), - Br,. 
The character of the salt Levy confirmed, but 
its formula should be 6K,Pt(CN),-K,Pt(CN), 
- Br,. Levy also found that when the cyano- 
SCIENCE 
931 
platinite is oxidized by lead or manganese 
dioxid in the presence of sulfuric acid, a sim- 
ilar compound is formed, but containing SO, 
instead of Br,, which behaves like the sulfate 
of a feebly electropositive element; in other 
words the group (7K,Pt(CN),) acts like a 
bivalent positive ion. More interesting was 
the result when hydrogen peroxid and other 
peroxids were used as the oxidizing agents. 
With the potassium cyanoplatinite there is 
at once formed a well-defined, crystallized 
double salt of the composition 3K,Pt(CN), - 
KPt(CN), - 6H,0, which is not further acted 
on by hydrogen peroxid. When, however, 
perhydrol is used the oxidation to KPt(CN), 
is complete, and a series of similar salts was 
prepared. With the free cyanoplatinous acid, 
H,Pt(ON),, the oxidation to HPt(CN), by 
hydrogen peroxid is complete. Here we have 
an acid and its salts in which the platinum 
acts, as in Wohler’s halid salts, as tri- 
valent, and its formula may be written 
HON -Pt(CN),. These cyanoplatinates would 
bear the same relation to the cyanoplatinites 
as the ferrocyanids bear to the ferricyanids. 
This is unexpected, as it would naturally be 
inferred that in accordance with the analogy 
furnished by the haloplatinites and haloplatin- 
ates, the cyanoplatinates would have the for- 
mula M,Pt(CN),. No evidence was found 
of similar compounds of the type 2MCN- 
Pt(CN), or 3MCN - Pt(CN),. On treatment 
with KON or with any alkali, decomposition 
ensued, with the regeneration of the cyano- 
platinite. J. L. H. 
SPECIAL ARTICLES 
SIMPLE DEMONSTRATION APPARATUS FOR THE 
INFRA-RED SPECTRUM 
Most teachers of experimental physics in 
this country do not attempt to illustrate the 
optical properties of matter in the long wave- 
length invisible spectrum, for the reason that 
the standard detecting instruments, the bolom- 
eter, thermopile, radiometer or radiomicrom- 
eter, are not particularly well suited for use 
in the lecture room where great stability is 
not usually ensured. Moreover, unless the lec- 
