822 
MR J. M. WORDIE ON THE NATURAL HISTORY OF PACK-ICE 
from the same physical properties in fibrous ice. This was to be expected, and does 
not call for detailed mention. 
Experiments were made from time to time to determine the specific gravity of 
the various types of sea-ice, and to discover especially if there was any relation 
between specific gravity and the amount of chlorine present. On the whole the 
results were not as satisfactory as they might have been, and, under the circum- 
stances, were of course incomplete. There is good ground, however, for supposing 
that something may eventually be gained from them. The method used was that 
recommended by Mr James, who himself made a good many of the determinations. 
The sample of ice was first of all weighed in air, in a temperature which varied from 
— 4° to — 12° C. (and which of course was not quite the same as that to which the 
ice had been exposed in situ ) ; it was then weighed in paraffin whose specific gravity 
and coefficient of expansion were known ; and the result calculated accordingly. 
In a previous paper it was stated that the specific gravities of fibrous ice ( i.e . ice 
showing vertical striae) clustered round 0'92, whilst those of comparatively pure 
spotted ice were nearer 0'91. This was a somewhat hasty conclusion to draw from 
the results. At the time Dr Otto Pettersson’s paper “ On the Properties of Water 
and Ice ” had not come to notice. The very numerous references to contraction 
cracks in Polar literature made it appear that sea-ice below its freezing-point behaved 
like pure ice, and contracted on cooling — the exact opposite to Pettersson’s con- 
clusions. Inasmuch, therefore, as the determinations of specific gravity were made 
with the ice varying in temperature from —4° to —12° C., the possible expansion 
according to Pettersson would be nearly 2 per cent., and all figures have, therefore, 
had to be re-examined. What has been done is to plot the specific gravity against 
the temperature of the ice at the time it was weighed. The result for fibrous ice 
shows a grouping of the values along lines which are perhaps comparable to 
Pettersson’s curve. In the case of spotted ice, however, there are many serious 
discrepancies ; but as this type contained considerably less salt than fibrous ice, 
it is quite natural to expect that its coefficient of expansion approximates rather to 
that of pure ice than to that of young-ice. 
Leaving aside spotted ice, and considering only the platy or fibrous type, our 
measurements showed that its specific gravity was 0‘92 at — 4° C. and 0'915 at — 15° C. 
The amount of chlorine present was about 3 per cent. These figures indicate the 
same order of things as Pettersson puts forward, but of a very different magnitude. 
Between — 4'4° and — 6'4° C. he found an expansion of 0'002957 (i.e. more than three 
times the Endurance result) for ice of a kind which seems to be the same as the 
ice spoken of here as fibrous. The method used in the Endurance , however, was 
not sufficiently exact to merit more weight being attached to the results got by it 
than to Dr Pettersson’s made in the laboratory. Even if they could be, any dis- 
crepancy could be easily explained by the fact that practically no two pieces of ice 
are identical. 
