In practice it is seldom found that any one of the numerous grades of oil prepared from crude petroleum is a satisfactory mosquito larvicide. The final product is almost invariably blended from several constituents. Each of the constituents may confer beneficial properties on the larvicide directly, or it may serve to correct undesirable features possessed by the other ingredients.

Even under world conditions which might be regarded as normal compared with those prevailing to-day, difficulties have confronted those who wished to select or blend a larvicide. There was firstly, in the remoter parts of the world, a lack of any specialised chemical apparatus ; secondly, the lack of a complete minimum performance specification by which to judge laboratory blends ; and thirdly, the difficulty arising from the fact that the specifications supplied for commercial grades of oil do not include data on many properties of the oil which are important to the malariologist but unimportant to the usual consumer.

This paper represents an endeavour to overcome the three difficulties outlined above. It provides a minimum performance specification for a larvicide and describes a series of simple tests which may be applied (a) to a commercially blended larvicide in order to establish whether this meets the requirements of the specification, and (b) to the individual ingredients (e.g., kerosines, Diesel oils or fuel oils) so that, in each case, the one with the most desirable combination of properties may be selected for incorporation in the final blend.