JULY 23, 1897.] 
give an atomic weight of 139.05, or about 
one unit lower than the best previous de- 
termination. According to this last weight, 
cerium is a member of the first series of 
Mendeleff’s fourth group, and to this the 
oxid CeO, corresponds. It is true that 
many of the properties of cerium do not 
agree well with this position, but the atomic 
weight of 92.7 can hardly be brought into 
harmony with the periodic system, as there 
_is no vacant place between zirconium (90.4) 
in the fourth group and columbium (93.7) 
in the fifth group. 
E. Cauarp, in the Comptes Rendus, sug- 
gests the use of calcium carbid as a phyl- 
loxericide. The presence of phosphorus in 
the carbid is advantageous, as the phospho- 
carbid possesses exceptionally powerful in- 
secticidal properties, probably owing to the 
generation of acetylene rich in phosphin, or 
possibly containing a phosphorus-carbon 
compound. 
A RECENT number of Nature contains a 
notice, taken from the Journal of the Rus- 
sian Physical and Chemical Society, of the 
death of Dr. Véra Bogdanovskaya-Popoff, 
who was killed on May 8th in her labora- 
tory at Izhora by an explosion. She had 
been working to obtain a compound of car- 
bon and phosphorus, analogous to prussic 
acid, but with phosphorus in the place of 
nitrogen,and it was while engaged in this 
dangerous investigation that the fatal ex- 
plosion occurred. 
In a paper read before the Royal Society 
on June 17th, W. J. Russell describes the 
action excited by certain metals ard other 
substances on a photographic plate. Ex- 
periments showed that uranium salts and 
oxids act slowly on photographic plates in 
the dark; this property is shared by me- 
tallic zinc, cadmium and magnesium, as well 
as many other substances, as copal, straw- 
board, wood, some kinds of paper. This ac- 
tion was at first supposed to be contact ac- 
SCIENCE. 
125 
tion, and then it was thought that in the case 
of metals minute emanations might be given 
off. This, however, is negatived by the fact 
that zine acts equally well when not in con- 
tact with the plate, and even when com- 
pletely insulated by a coating of varnish. 
Tue June Journal of the Chemical So- 
ciety contains a paper by Dr. John Ball on 
the circumstances which affect the rate of 
solution of zinc in dilute acids, with especial 
reference to the influence of dissolved me- 
tallic salts. It is a familiar fact that the 
action of pure zinc on sulfuric acid is very 
slow, but may be greatly accelerated by the 
addition of certain metallic salts. Platinic 
chloride is generally used for this purpose, 
and less frequently a cobalt salt. Dr. Ball 
finds that with sulfuric acid, magnesium or 
aluminum sulfate have no accelerating in- 
fluence, that of chromium, manganese and 
iron is very slight, silver is greater, while 
cobalt, copper and nickel sulfates have 
great influence and in this order. The 
relative maximum velocity of solution, tak- 
ing the velocity of pure sulfuric acid as 
unity, is for the addition of silver sulfate, 
9; cobalt sulfate, 18; copper sulfate, 21, 
and nickel sulfate, 38. In thecase of solu- 
tion in hydrochloric acid the addition of 
manganese, lead or tin chloride had but 
little influence, copper somewhat greater 
(11), while the relative velocities for cobalt, 
gold, platinum and nickel were respectively 
31,39,42 and 45. It will be seen that with 
both acids the addition ofa nickel salt causes 
the greatest acceleration, and the relative 
order of the different methods is approxi- 
mately the same, except that copper has 
much less influence on the solution in hy- 
drochloricacid. Dr. Ball presents no theory 
of the reaction, but it isa fact worthy of 
note that in the case of the two metals 
having most decided influence, nickel and 
cobalt, it could not be detected that any 
metal was deposited on the zinc, thus form- 
ing a couple. J. L. H. 
