378 Mr. T. J. Herapath on some Combinations of 



however, of obtaining this glass free from air-bubbles, I was 

 unable to ascertain its true specific gravity. It was slightly 

 superior to flint-glass in hardness. 



The hydrated salt, dried for some time at 212^ F., yielded 

 upon analysis the following numbers: — 



I. 10 grs., when heated to redness, lost \'519 grs. in weight 

 = 15*790 per cent. 



II. 25 grs., treated as before, lost 4'021 grs. in weight 

 = 16"084< per cent. 



III. 10 grs. gave of PbO, SO^ 7*07 grs. = PbO 5-2095 

 = 52-095 per cent. 



IV. 25 grs. gave of PbO, SO' 17-784. grs. = PbO 13-1040 

 = 52*4' 16 per cent. 



I. II. III. IV. Mean. 



Water . . . 15*790 IS-OSi ... ... 15*9370 



Oxideoflead. ... ... 52-095 52*4.16 52*2555 



Boracic acid , ... ... ... ... 31*8075 



Now, supposing its composition to be expressed by the for- 

 mula PbO, 2BO^ + 4HO, it ought to be composed of— 



Water 4 36 or 16*513 per cent. 



Oxideoflead. . . 1 112 ... 52*376 

 Boracic acid ... 2 70 ... 32*111 



Dried between 400° and 450*^ F., it contains 4*435 per cent, 

 of water=one atom ; calculation requires 4*712 per cent. • 



NitrO'Borate of Lead. — When either of the above-described 

 borates of lead are dissolved in moderately strong nitric acid 

 to saturation, the solution filtered and concentrated by evapo- 

 ration until a pellicle appears upon the surface, and then 

 allowed to cool, the sides of the vessel containing the solution 

 in a short time become covered with numerous irregular, 

 glistening crystals. These, when heated to somewhat above 

 250° F., become nearly opake, slightly decrepitate, and give 

 off water and traces of nitric acid vapour. Heated to redness, 

 they evolve large quantities of nitrous acid fumes, and the re- 

 sidue fuses into a transparent colourless glass. They are, 

 therefore, obviously a nitro-borate of lead; but from the dis- 

 cordant results of my analyses, I have as yet been unable to 

 satisfy myself with regard to their true composition. They 

 are most probably composed of PbO, BO^, -f PbO, NO^ 

 + HO. 



Chloro-Borate of Lead. — This curious and interesting double 

 salt was formed accidentally whilst attempting to prepare a 

 borate of lead by precipitating a hot solution of biborate of 

 soda by a boiling concentrated solution of chloride of lead. 

 By filtering the mixed solutions whilst still warm, and wash-. 



