92 The Phosphates of America. 



The surest means of accurately knowing what is going on in 

 the chambers is afforded by the provision and maintenance in 

 proper condition of " drips " and " caps." This is a well-estab- 

 lished fact among old and experienced acid-makers universally. 



The best apparatus for taking drips consists of a small lead 

 dish placed within the chamber upon a 15-inch diameter earthen- 

 ware pipe, about 3 feet high, and at about 1^ feet from the side. 

 A small half-inch lead pipe, shaped like an S, is fixed into the bot- 

 tom of the dish and pierces the chamber side, setting with its 

 mouth over a leaden basin standing upon a leaden ledge outside. 

 The liquid acid passes as it is formed through the siphon, drips 

 into the basin and, overflowing upon the ledge, is carried back 

 again into the chamber by a small pipe. 



Two drips should be arranged in each chamber of the set, 

 at equal distances from each other, and the contents of the basins 

 will constantly represent the nature of the acid and indicate 

 its strength, nitrosity, etc., at any moment. Certain openings 

 should be left in each chamber ; a man : hole, and a small hole near 

 the end for sampling. A couple of windows will also be useful, 

 one fixed in the darkest side, about five feet from the ground, and 

 the other in a direct line with it upon the top. 



The light shining through these windows reveals to an experi- 

 enced eye the exact condition of the gases. 



The following indications are furnished by the caps of the 

 chambers as to w T hat is going on within, and are worthy of note : 



When one of those covering the first chamber is slightiy lifted 

 the gases should rush out with great force. This should become 

 less noticeable or almost disappear in the second chamber. 



If the inside of the cap be quite dry and covered with small 

 crystals, whjch, upon being moistened, turn green, the evidence is 

 certain of an insufficiency of steam. 



If, on the contrary, it be dripping wet, it is equally certain that 

 the steam is in excess, and in either case the remedy is obvious 

 and at hand. 



The regulation of the supply of nitre, after that of the draught, 

 is an extremely important point, a mismanagement inevitably en- 

 tailing one of two evils : 



First. If the quantity supplied be too large it ruins the lead 

 and excludes all possibility of profitable working. 



Second. If the quantity be too small there is an inevitable 

 escape of sulphurous acid. 



