Determinations have been made of the moisture contents of whole palm kernels kept for times up to 35 days in desiccators over saturated salt solutions for which the relative humidities a t 30' are known. The temperature fluctuated between 24' and 31".Factors which must be considered in the drying of foodstuffs are discussed. The conventional hot-air drying and the vacuum contact-plate drying methods are described and compared. The latter yields better dried products than the former, both in appearance and palatability of the reconstituted, cooked material, and there is some evidence that the storage properties are also improved. Relevant factors are the absence of oxygen and the milder heat treatment of the foodstuff during vacuum contact-plate dehydration. This technique is versatile and may be used to dry a wide range of commodities, many of which cannot be dried satisfactorily by conventional methods.

Many thousands of tons of bagged, decorticated groundnuts are stored for periods of up to 15 months in warehouses in Kano, Northern Nigeria. A large indigenous population of Tribolium castaneum (Hbst.) infests the stored nuts and considerable losses are caused. In 1948, investigations into the control of this and other pests by means of insecticides were commenced. As a result of these trials (Howe, Hayward & Cotterell, 1952) a routine programme of control measures was evolved, based upon the application of y BHC as a water-dispersible powder at monthly intervals. Subsequent observations indicated that large numbers of T. castaneum were present within two weeks after spraying and preliminary experiments suggested that the probable cause was the inadequate persistence of BHC under the climatic conditions prevalent in Northern Nigeria.Eecent intensification of the control measures necessitated a more accurate knowledge of the persistence and toxicity of y BHC at different rates of application under conditions in Kano. Experimental Techniques. General methods.In the preliminary trials, circular discs of sacking were pinned to the surfaces of stacks of bagged groundnuts in a warehouse. A 25 per cent, water-dispersible lindane formulation was applied uniformly over the stack by means of a pressureretaining knapsack-type sprayer. Despite careful application under still conditions the deposits obtained varied from 20 to 47 mg. y BHC per sq. ft.An attempt was then made on a laboratory scale to obtain more uniform deposits by means of a small hand atomiser of the scent-spray type operated by depressing a small plunger. A constant volume of a suspension of 50 per cent, lindane dispersible powder in water was applied to filter papers, but the rate of settling of the suspension resulted in widely varying initial deposits.Eventually it was found that consistent initial deposits could be obtained on filter papers by applying the y BHC in a volatile organic solvent by means of the hand atomiser. This was designed to deliver a constant volume, the rate of application being controlled by varying the strength of the solution. Even, using this technique only a proportion of the actual volume delivered was obtained as a recoverable deposit on the filter papers. With carefully controlled conditions, however, this proportion was sufficiently constant to enable up to a hundred papers to be treated with little variation of initial deposit using the same dosage rate. This may be termed the spraying factor for the particular set of conditions and the accurate knowledge of this factor enabled the following technique to be adopted in all the experiments.A specimen of lindane of melting-point range 109-5-113°C. was prepared by recrystallisation in petroleum ether solution from a 50 per cent, formulation. Initial deposits of approximately 10, 20 and 40 mg. of lindane per sq. ft. were

I t was found by counting the total number of external bags in a pyramid that on the The average total contamination average they comprise 26% of the total bags present. throughout the pyramid is therefore 2% 26 ---x -= 0.173~. 100After the spray had dried, specks of DDT were discernible on the outer surfaces of the sacks and it was not expected that much would be absorbed. The figures, however, show that a considerable proportion of the insecticide in fact was absorbed after six months' storage. BHC did not show obviously on the sacking and it appeared to be absorbed by the produce to a greater degree than DDT. l h e fairly strong characteristic odour associated with commercial HHC was noticeable in the vicinity of the pyramid some weeks after spraying, but no undesirable flavour or odour could be detected in the unexpressed nuts and samples of cake and oil after storage.As the levels of spraying in these tests were more than double those which have been used in routine spraying it was concluded that there was no likelihood that the tentative limits for BHC and.DDT in foodstuffs would be approached by spraying at levels normally used when a whole pyramid is considered. Individual external bags may, however, contain relatively high concentrations. Very considerable mixing of internal and external bags occurs during breaking down pyramids and loading rail wagons, in addition to that during porthandling in Nigeria and the receiving country.