Under summer conditions, such as were contemplated, when there was less cold for the men to endure, and less firing needed to melt the snow for cooking, the fullest allowance of oil was 1 gallon to last a unit of four men ten days, or 1/40 of a gallon a day for each man.
The amount allotted to each unit for the return journey from the South was apparently rather less, being 2/3 gallon for eight days, or 1/48 gallon a day for each man. But the eight days were to cover the march from depot to depot, averaging on the Barrier some 70-80 miles, which in normal conditions should not take more than six days. Thus there was a substantial margin for delay by bad weather, while if all went well the surplus afforded the fullest marching allowance.
The same proportion for a unit of five men works out at 5/6 of a gallon for the eight-day stage.
Accordingly, for the return of the two supporting parties and the Southern Party, two tins of a gallon each were left at each depot, each unit of four men being entitled to 2/3 of a gallon, and the units of three and five men in proportion.
The return journey on the Summit had been made at good speed, taking twenty-one days as against twenty-seven going out, the last part of it, from Three Degree to Upper Glacier Depot, taking nearly eight marches as against ten, showing the first slight slackening as P.O. Evans and Oates began to feel the cold; from Upper Glacier to Lower Glacier Depot ten marches as against eleven, a stage broken by the Mid Glacier Depot of three and a half day's provisions at the sixth march. Here, there was little gain, partly owing to the conditions, but more to Evans' gradual collapse.
The worst time came on the Barrier; from Lower Glacier to Southern Barrier Depot (51 miles), 6 1/2 marches as against 5 (two of which were short marches, so that the 5 might count as an easy 4 in point of distance);from Southern Barrier to Mid Barrier Depot (82 miles), 6 1/2 marches as against 5 1/2; from Mid Barrier to Mt. Hooper (70 miles), 8 as against 4 3/4, while the last remaining 8 marches represent but 4 on the outward journey. (See table on next page.)
At to the cause of the shortage, the tins of oil at the depot had been exposed to extreme conditions of heat and cold. The oil was specially volatile, and in the warmth of the sun (for the tins were regularly set in an accessible place on the top of the cairns) tended to become vapour and escape through the stoppers even without damage to the tins. This process was much accelerated by reason that the leather washers about the stoppers had perished in the great cold. Dr. Atkinson gives two striking examples of this.
1. Eight one-gallon tins in a wooden case, intended for a depot at Cape Crozier, had been put out in September 1911. They were snowed up; and when examined in December 1912 showed three tins full, three empty, one a third full, and one two-thirds full.
2. When the search party reached One Ton Camp in November 1912 they found that some of the food, stacked in a canvas 'tank' at the foot of the cairn, was quite oily from the spontaneous leakage of the tins seven feet above it on the top of the cairn.
The tins at the depôts awaiting the Southern Party had of course been opened and the due amount to be taken measured out by the supporting parties on their way back. However carefully re-stoppered, they were still liable to the unexpected evaporation and leakage already described. Hence, without any manner of doubt, the shortage which struck the Southern Party so hard.