278 MANITPACTURE OF NITRATE OP SODA. 



become damaged, perhaps beyond repair, losing their original 

 lines by subsidence, and thus fracturing the steam and other 

 connections resting on them. 



In making the foundations for the carrying walls, which 

 are constructed of trimmed igneous boulders found in the locality, 

 the ground was excavated to a depth of 12 feet, over an area of 

 7,500 square feet, although the walls are only 84 feet long, and 

 29 feet apart from outside to outside. A layer of broken 

 boulders 2 feet deep was first deposited, and a filling of one- 

 third Portland cement, one-third sharp sand, and one-third 

 hydraulic lime, was run in the interstices. Next a layer of con- 

 crete, made of hard stone, of about 1-inch cubes, with one-half 

 cement and one-half sand, was superposed 1 foot deep, and then 

 three layers of good masonry all cemented. On this the walls 

 were built, 12 feet high, 6 feet wide at the base, and 3 feet 

 6 inches at the top. This apparently excessive batter is neces- 

 sary as a safeguard against the frequent earthquakes, which 

 often cause much damage to machinery constructed on weak, 

 straight, or high foundations. A wooden framing of Oregon 

 pine, with the uprights and runners 1 foot square, the uprights 

 being 5 feet 6 inches from centre to centre, was next built, on a 

 wall 2 feet 6 inches high by 2 feet 6 inches thick, in the centre 

 of the space between the two main walls, and parallel to them, 

 in order to obtain a good distribiition of the weight of the 

 boiling tanks. On this framing twenty-four iron girders, 10 

 inches wide, 10 inches deep, and 35 feet long, were laid, and on 

 the top of the girders the boiling tanks were bolted in sections 

 and riveted. The inside carrying- wall is backed up by cemented 

 masonry, 6 feet high and 4 feet wide, with an inward sloping 

 surface, so as to catch any drainage or leakage from the ends 

 of the tanks, from whence it flows into the passage between the 

 two main walls by means of ten drains or conduits of 3-inch 

 pipe built in the main wall. From the north to the south end 

 of the floor between the walls there is a fall of 6 inches, causing 

 all the drainage to flow to the south end, where a canal and 

 tank are provided for its reception. Three parallel walls are 

 built in front of the main walls, on which the washing tank, 

 consisting of five compartments, each 24 feet by 6 feet 6 inches, 

 rests. 



