128 BACTERIA IN RELATION TO PLANT DISEASES. 



tinned-copper gasket. The steam which runs the apparatus is brought to the lab- 

 oratory floor through a i;^-inch pipe, in which (in the engine room) there is a 

 steam gage registering up to 150 pounds, and a reducing valve set at 55 pounds. 

 This very considerabl}' lessens the steam pressure in the copper coil, moderates the 

 violence of the ebullition, and makes the apparatus perfectly safe. The hydrant- 

 water outflow pipe (flush) to the sewer, for occasionally washing out accumulated mud 

 (4) passes from the bottom of the boiler immediately above fig. 19. Gate- valves 

 are used. All brass and copper parts in contact with the steam are tinned; all 

 metal parts in contact with the distilled water are tin, tinned, or nickel-plated. 



With 60 pounds steam pressure in the engine-room boiler, 40 pounds pressure 

 at the reducing valve, 35 pounds pressure in the pipe at the laboratory floor near 

 where it enters the still, and one-half pound pressure or less in the steam chamber 

 above the coil of copper pipe, the capacity of this still is 60 liters (16 gallons) per hour. 



The apparatus must be built ^'ery substantially in all parts, so as to withstand 

 at least twice as much steam pressure as any part of it will be subjected to, e. g., 160 

 pounds in the iron pipes and in the copper coil and its attachments, and at least 20 

 pounds in the catch basin, and other parts subject to steam generated in the still. 

 A steam gage, in addition to the one in the engine-room, shows the pressure in 

 the coils, and another the pressure in the steam chamber above the coils. They are 

 not shown in the plate, as they were put on after that was made. The former is 

 attached to the steam supply pipe near the floor, and the latter to an ann of the 

 safety-valve pipe. The boiler should be taken down and the parts retinned once a 

 a year, or at least once in two years. 



If a much greater quantity of water is needed the block-tin condensation coil 

 should be lengthened to 60 feet, the diameter of the inflow pipe of the condenser 

 should be increased to 2 inches, and the outflow pipe to 2 ^ inches, and the cubic 

 contents of the condenser tank should be quadrupled. The capacity of the bath-tub 

 (or other receptacle), for a large laboratory should be at least 500 liters, and might 

 well be 1,000 liters. 



The above apparatus has been in use for two years. It works very smoothly and 

 satisfactorily when the proper amount of steam is let into the coil of copper pipe, 

 which ordinarily should not be nearly the whole amount available. The inflow of 

 steam is governed by the valve a few inches below fig. i in plate 14. When 

 too much steam enters the coil, the pressure in the steam chamber above it rises to 

 five pounds or more, hot water is forced back through the feed pipe (3) into the 

 neighboring pipe which furnishes cold water to the condenser (12), and steam in- 

 stead of distilled water is furnished to the water tank. This is at once obviated by 

 cutting off" part of the steam inflow and moderating the force of the boiling. It 

 might also be obviated by reducing the length of the arm of the safety valve (9) 

 which in any event should not be weighted. 



Sufficient water for small quantities of culture-media and pure enough for most 

 purposes may be obtained from the simple glass still shown in fig. 82 by one dis- 

 tillation. Water of a high degree of purity may be obtained by two distillations, 

 adding 0.5 gram to i gram of potassium permanganate per liter of water before the 



