294 
MR. W. CROOKES ON THE ATOMIC WEIGHT OE THALLIUM. 
Nominal value 
of weights. 
True value in air at 
30 in* 62° F. 
Weight of air 
displaced. 
Volume in water of 
maximum density. 
grs. 
grs. 
S r - 
grs. 
1000-00 
1000-000000 
0-058271 
47-5100 
600-00 
599-998340 
0-035533 
28-9700 
300-00 
300-000240 
0-017501 
14-2700 
200-00 
199-998910 
0-011664 
9-5100 
100-00 
99-991420 
0-005887 
4-8000 
60-00 
59-993232 
0-003483 
2-8400 
30-00 
29-999991 
0-001668 
1-3600 
20-00 
19-999984 
0-001104 
0-9000 
10-00 
9-998477 
0-000490 
0-4000 
6-00 
5-998268 
0-000355 
0-2900 
3-00 
3-000469 
0-000171 
0-1400 
2-00 
1-999839 
0 000113 
0-1000 
1-00 
0-998980 
0-000055 
0-0400 
0-60 
0-602350 
0-000035 
0-0300 
0-30 
0-303600 
0-000017 
0-0200 
0-20 
0-203240 
0-000011 
0-0100 
0-10 
0-098110 
0-000005 
0-0040 
0-06 
0-061472 
0-000003 
0-0030 
0-03 
0-030561 
0-000002 
0-0020 
0-02 
0-022884 
0-000001 
0-0010 
0-01 
0-014097 
0-000001 
0-0004 
0-01' 
0-009997 
0-000001 
0-0004 
0-01" 
0-009967 
0-000001 
0-0004 
The value of each weight in air, plus the weight of air displaced, is, of course, the 
weight in vacuo. 
Having ascertained their true value, the weights were carefully preserved ; and as, 
being of platinum, there was no accumulation of tarnish on their surface, and as they were 
lifted with ivory- tipped forceps to prevent wear, they have showed up to the present 
time, whenever compared, absolutely no alteration. 
The Glass. 
The flasks and vessels used were of the hardest Bohemian glass, and as thin as they 
could be employed. When practicable, vessels of old green German glass were used; 
neither this nor Bohemian glass is practically affected by reagents. 
Liquids were generally kept sealed up in glass bulbs and globes, but sometimes in 
stoppered green German glass flasks or in “ bromine” bottles. When liquids were kept 
in these bottles for a few days only, they were not found to have contracted any saline 
impurity from the glass, but after remaining for some weeks they were found to leave a 
visible residue on evaporation. 
No cork or luting was employed in the distillations &c. ; in most cases the appa- 
ratus was blown in one piece, and the operations performed in a vacuum. The pieces of 
apparatus which were weighed were entirely composed of glass suspended with plati- 
num loops. The fingers were not allowed to touch them after the first weighing. 
The weight of tubes, bulbs, and flasks, even of hard Bohemian glass, constantly dimi- 
nishes when the glass is long heated in a spirit- or gas-flame ; this loss may amount 
* The cistern of the barometer is 115 feet above the approximate mean water-level at Somerset House. 
