540 ON THE DESTRUCTION OP NOXIOUS INSECTS 



soil mixed with some vegetable mould, and the roller is slightly applied 

 to it. Every five or six days the watering is to be renewed in order to 

 facilitate the germination. 



At the end of about 30 or 40 days the young plants make their 

 appearance and as soon as they have gained strength enough they are 

 transplanted. Three months after, they are transplanted again at wider 

 distances according to their strength, each time being of course watered, 

 but only moderately. 



The blossoming commences in the second year towards the end of 

 May and continues to the end of September. Within that period the 

 heads from which the powder is made must be gathered. The most 

 favourable time for gathering seems to be when the heads are about to 

 open — that is, when the flowerets of the circumference are yet standing 

 erect. In this state the fecundation takes place, and the essential oil 

 contained in the heads has reached its highest state of development. 

 The stalks and leaves through having the properties in a less degree, 

 may be used also for making powder, but they must be mixed with the 

 flowers in the proportion of a third of their weight. The powder thus 

 obtained will perfectly answer the destruction of insects. Towards the 

 end of September, at which time the blossoming has ceased, the stalks 

 are cut at about 4 inches from the ground. As the flowers are cut they 

 are dried in a granary or shed, great care, however, being taken not to 

 expose them to moisture or to the rays of the sun. When completely 

 dried the flowers are to lie hermetically closed up in sacks, so as to 

 prevent too early pulverization. In pulverizing them it is better not to 

 take a larger quantity than the wants of the moment may require. The 

 volatilization, which is of course more rapid in the powdered lorm than 

 in flowers, will thus be avoided. It has been suggested that the drying 

 of the flowers for making the powder might be effected on sheet-iron 

 plates, like tea leaves are dried in China, but this operation is most 

 injurious to the plant, dissipating the essential oil. 



Pulverization. — Among the numerous methods which we have tried 

 in order to simplify the pulverization of the dried flowers, that which 

 appears the best is to pound the flowers in a mortar. The mortar should 

 be covered with a piece of leather, through which the pestle moves, 

 adjusting it in such a way as to prevent any contact from without, 

 as is usually done in pulverizing drugs in a laboratory. The 

 quantity to be pulverized should not exceed a pound at a time 

 thus avoiding too high a degree of heat which would be injurious to the 

 quality of the powder. The pulverization being deemed sufficient, the 

 substance is sifted through a silk sieve, and the residue, with a new 

 addition of flowers, is put into the mortar and pulverized again. 



This method of preparation is so simple as to be within the reach 

 of all ; the pulverization by steam is more rapid and effectual, but 

 necessarily more expensive. The best receptacles for holding the 

 powder seem to be bottles, these, if well corked, will keep out moisture 



