Dr. Samuel Darling, of the laboratory, finally worked out a mixture of carbolic acid, resin and alkali, which would emulsify in water and accomplish this purpose. The mixture was known as larvacide. The method of its manufacture was as follows: One hundred and fifty gallons of crude carbolic acid are heated in an iron tank having a steam coil, with steam at fifty pounds pressure. Two hundred pounds of finely crushed and sifted common resin are dissolved in the heated acid, and thirty pounds of caustic soda dissolved in six gallons of water are added. There is a mechanical stirring rod attached to the tank. The product is ready in a few minutes, yielding about three and one-half barrels. COST OF MANUFACTURE, AUGUST, 1909. _Amount manufactured: 14,600 gallons (292 barrels)_ 12,600 gallons crude carbolic acid at 12 cents per gal. $1,512.00 12,300 pounds rosin at $2.48 per hundred 305.04 2,550 pounds caustic soda at $3.70 per hundred 94.35 2 tons coal at $5.00 per ton 10.00 Labor 94.46 Supervision. 50.00 ———————— Total $2,065.85 Cost per gallon 14.14 To insure the manufacture of a uniform product, requisitions called for crude carbolic acid of a specific gravity not greater than 0.97, and to contain not less than 15 per cent tar acids. Each consignment of crude carbolic acid received was assayed at the laboratory to determine its specific gravity and percentage of tar acids, for it is necessary to keep the product of a specific gravity approximately that of water, so that it will diffuse rapidly and neither sink to the bottom, nor remain at the surface. In a hundred square miles of territory treated we used about two hundred barrels of this mixture a month. The cost of manufacture was about seventeen cents a gallon. In the early days we had used various proprietary articles for this purpose, for which we generally had to pay about fifty cents per gallon. Larvacide came in the course of time to be used on the Isthmus for disinfectant purposes of many kinds, and also for the prevention of fly-breeding. We found it most excellent for all rough purposes of this kind, such as disinfecting and deodorizing around privy vaults and similar places.