CARRIAGE OF FRUIT.

Otago Daily Times, Issue 19697, 26 January 1926, Page 4

CARRIAGE OF FRUIT.

VENTILATION OF SHIPS' HOLDS. INTERESTING EXPERIMENTS. (FfiOM Owe Own Co«nßß*>o}u>E}«?.) LONDON, December 11. It had already been known from previous observations that carbon dioxide gas leaks in considerable amounts from ship's holds carrying fruit overseas. Indeed, it was beoauso of this leakage that any successful shipments were made when no deliberate ventilation wa« given. Interesting experiments have been made by the Low Temperature Research Station, Cambridge, with the object of determining whore the gas leaked out. how it leaked (by mass movement or diffusion), and to what extent the leakago varied from ship to ship, and under different conditions. Direct leakage tests were made oh two vessels with holds of the "unventilatcd" grid type. Carbon dioxide gas was introduced into the empty holds, and thereafter by analysing the gas from day to day, the amount of leakage was determined. Experiments were made on two different ships. The first of these boats, A, had only jusi then been equipped for the carriage of refrigerated cargo j the second. Bj had been so equipped when originally constructed, and her hatcnes and insulation showed some signs of Wear and tear. One hold of each vessel Was investigated. In the former vessel the results indicated a leakage on the average of about 3500 cubio feet per day; that is to say, 3500 cubic feet of the "foul air" of the hold escapes, andi is replaced by a similar quantity of fresh air from outside the hold. In the case of vessel B the results indicated a leakage on the average of between 1300 and 1400 cubic feet of air per clay. It will be seen that the leakage from the newly insulated ship, which was expeotod' to prove more gas-light, was two and a-half times loss than that from tho old ship. METHOD OF,LEAKAGE, Further experiments to ascertain the method of leakage suggested that tho main leakage was occurring through the roof of the hold, producing in Ihis region a stratum of relatively fresh air of fluctuating composition and depth, The exceptionally low and irregular readings of the top centre sample suggested that the leakage occurred by that hatch rather than through the remainder of the roof of the hold. Tho results also showed clearly that there was no considerable esnipo of gas through the riveted structure of the hold, but that extensive leakage occurrpd through all the wooden ventilator plugs. Gas passed freely by tho bilge limbers into the bilge, but did not appear to escape further in this direction. No cvidenco was obtained of the pa*.ia#e of gas through the metal plaUv; of the bulkheads or decks. EFFECT OF STRONG WIND. An attempt, was made to measure the wind velocity On the ship's deck and «. surprising result was obtained. Although a strong breeze was blowing across the harbour in the direction from starboard to port, of the ship, the air on the ship's deck and immediately over the hatch was moving slowly (20 to 40 Feet per minute) in tho opposite direction, from port to starboard. Further examination s-howed _ that the wind, on striking tho starboard side at the ship, was deflected upwards. This vigorous up-draught presumably created an afea of low pressure on the .starboard side of the sbip-'a deck, which caused a£r iff La

drawn ov«>r the hateh from port to starboard. Such vigorous draughts as these would have a- marked effect on the leakage from the holds. 'Hie outstanding 1 fact revealed by the investigation is that the rate of leakage of gas actually observed from the holds in port is very much less than the rate necessary to provide for the escape of the gas produced by a' oarsto of fruit where thero are no other means of ventilation. The necessary leakage for successful apple carriage is of the order of 25 cubic feet of air per. day per ton of fruit; such a leakago will suffice to keep the concentration of carban dioxide in the hold at the safe limit of 10 per cent.