Boracic Acid with Oxide of Lead. 377 



to 500*' F., it may be rendered perfectly anhydrous without 

 experiencing any perceptible change of colour. 



Sesquiborate of Lead, 2PbO + 3BO^. — The salt which is 

 produced when a boiling solution of the nitrate, or any other 

 soluble salt of lead is precipitated by a great excess of bibo- 

 rate of soda, has been hitherto considered by chemists to be 

 composed of PbO + SBO^. According to my experiments, 

 however, it would appear to consist of 2PbO + SBO^. It is a 

 white powder, like the preceding, which it closely resembles 

 in its properties. Before the blowpipe it fuses into a colour- 

 less glass, the specific gravity of which is rather lower than 

 that of the neutral borate, being 5*2352; its hardness is very 

 nearly equal to that of flint-glass. The following are the re- 

 sults of my analysis of this salt dried at 2] 2'^ F. : — 



I. 10 grs., heated to redness, lost 0'918 gr. in weight 

 = 9-1800 per cent. 



II. 11-26 grs., treated as before, lost 1-106 gr. =9-8223 

 per cent. 



III. 25 grs. lost 2-3 grs. in weight=9-2000 per cent. 



IV. 10 grs. gave of PbO, SO^ 8-62 grs.= PbO 6-3515 

 = 63-5150 per cent. 



V. 10 grs. gave of PbO, SO^ 8-34 grs. = PbO 6-14.52 

 = 61-4520 per cent. 



VI. 10 grs. gave of PbO, SO^ 8-41 i grs. = PbO 6-1975 

 = 61-9750 percent. 



I. II. in. IV. V. VI. Mean. 



HO . 9- 1800 9-8223 9-2000 ... ... ... 9-4007 



PbO 63-6150 61-4520 61-9750 62-3140 



B03 ... ... ... 28-2853 



These numbers indicate a composition very closely approxi- 

 mating to the formula 2PbO, 3BO^ + 4HO, as will be seen 

 upon comparing them with those given below : — 



Water 4 36 or 9-8630 per cent. 



Oxide of lead . . 2 224 ... 61-3690 

 Boracic acid ... 3 105 ... 28-7680 

 Dried between 350° and 400" F., it loses two of its atoms of 

 water, and its composition is now expressed by the formula 

 2PbO, 3B03 + 2HO. 



I. 10 grs. of the salt in this state of hydration lost 0-495 gr. 

 upon being heated to redness, =4*9500 per cent.; calculation 

 requires 5-1873 per cent. 



Biborate of Lead, PbO + 2BO^, may be easily obtained by 

 boiling either of the preceding recently-precipitated salts, 

 whilst still moist, in a concentrated solution of boracic acid. 

 It is a light amorphous powder, which at a red heat fuses with 

 difficulty into a vitreous mass. From the almost impossibility, 



