The Phosphates of America. 97 



dish destined to receive the hot concentrated acid must be of twenty- 

 five pound lead and have a well-formed lip, a loose sheet of lead 

 being placed over its bottom to prevent injury from the linings. 

 The cast-iron gas-pipe leading from the furnace projects a little 

 above the dish some 8 or 9 inches into the tower, and directly be- 

 neath an arch built either of pure quartz or glass bricks, levelled up 

 with small lumps of pure silica or the broken -up ends of old bottles. 

 Upon this arch comes the packing, and here we enter into the 

 dangerous domain of discussion and disagreement, where, while 

 all managers agree in admitting the utility of the tower, all have 

 pet theories as to the manner in which it is to be lined and packed 

 in order to wear well and be turned to profitable account. 



In a tower which has now been continually at work for nearly 

 four years, and with which we are well acquainted, there are first 

 placed upon the arch about 8 feet of open packing, with first-class 

 fire-bricks, into the interstices of which is loosely distributed a 

 sufficient quantity of minute siliceous pebbles. 



Next comes about 3-J- feet of chemically clean and pure flints of 

 moderate size, and finally, up to within about five feet of the cover 

 (which, together with the distributing apparatus, is the same as 

 that described in the Gay-Lussac tower) come successive layers 

 of the best hand-picked hard-burned oven-coke. 



Immediately below the cover is an exit-pipe 3 feet in diameter, 

 leading to the chamber with a considerable fall, while upon the 

 top of the tower are two tanks placed side by side and suitably 

 covered, but accessible to the cooling influence of the air. Into 

 one of these tanks is pumped the whole of the acid from the Gay- 

 Lussac tower, as we previously remarked, and into the other all or 

 any part of the 50 B. acid from the lead chambers. 



Pipes lead from each tank to a reaction wheel under the cover of 

 the tower, whence, with the same cautious observance of minute 

 and equal distribution already insisted upon in the case of the 

 Gay-Lussac tower, the two liquids, made to meet and combine in 

 equal proportions, trickle downwards. 



We have seen that the acids from the chambers and the bottom 

 tanks must be continually hoisted to the cistern on the summit of 

 the towers, and it has been demonstrated that compressed air will 

 carry them to any height, while exercising no decomposing action 

 on the liquids. 



The description of siphon or " egg " (as it is commonly called) 



