160 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



Filter* for salt water. — There were located under the floor of the main building of 

 the Fisheries Exhibit two pressure filters of the Jewell patent, each 6 feet in diameter. 

 5 feet in height, connected to operate independently or together. The rated guaranteed 

 capacity of these two filters was 250,000 gallons in 24 hours. 



Daring the first month or two of the Exposition it was not found necessary to work 

 the filters to their rated capacity, but during warm weather they were frequently 

 worked beyond this capacity. The rate of filtration at some periods was as high as 

 750,000 gallons per day, and although the filters were taxed to this great extent their 

 work was satisfactory. 



The filters worked under a pressure ot 60 pounds to the square inch in the inlet, 

 and from 50 to 60 pounds in the discharge pipe; the difference in the pressures varying 

 according to the time the filters were in operation between washing, or in other words 

 with the accumulation of the impurities. 



The filter beds were composed of white machine-crushed quartz, and were 2 feet 

 4 inches in depth. 



The water before it entered the filters was treated by the addition of a very small 

 quantity of alum solution. The amount of alum used averaged about i of a grain 

 per gallon, or 1 pound for about every 30,000 gallons of water filtered. The expense 

 of this alum was about 2 cents per pound. 



The action of the alum upon the water was a chemical one, ana served to remove 

 the dissolved-coloring matters and invisible impurities, such as bacteria, etc., and it 

 also served to assist the retention of the extremely fine particles of suspended mat- 

 ters, which would otherwise pass through a filtering bed of the nature and porosity 

 of that which was used in the filters during a high rate of filtration. 



Analysis demonstrated that not the slightest trace of alum that passed through 

 the filters appeared in the filtered water. The apparatus used for introducing this 

 solution of alum was located about 150 feet from the filters on the inlet pipe, and 

 was exclusively an auxiliary apparatus. 



There were also located under the floor of the arcade, at the end nearest the 

 aquaria, two box filters, 12 feet long, 4 feet wide, and 2 feet deep, constructed of 2-inch 

 plank. These were filled with layers of coarse gravel and fine sand, through which 

 all the waste water from the aquaria was filtered before passing to the main reservoir. 



Apparatus for regulating the temperature of the fresh and salt water supplies.— For 

 the purpose of regulating the temperature of the water for the aquaria in summer 

 and winter, there were secured to the joists under the arcade two sections of 12-inch 

 wrought- iron pipe, each 20 feet long, and on the ends of each section were screwed 

 cast-iron caps. One of the caps on each section had two holes drilled in, to allow 

 2i-inch pipes to pass through. 



The section of 12-inch pipe used for the salt water contained four lengths of 

 drawn-brass pipe, 24 inches diameter and 20 feet long, tinned inside. These four 

 lengths of pipe were so connected as to form a continuous coil. The ends of these 

 coils passed through holes in one of the caps of each section, and were fitted with 

 inside and outside lock nuts, thus making the sections or reservoirs steam and watfl 

 Lght. 



These coils were afterwards connected, by proper valves, to the supply pipes tig 

 aquaria, and were so arranged that the supply water for the aquaria, could be made 

 to pass through these coils if necessary. 



