282 DECOMI^OSIXrOX Of PHOSPHATES BY CHARCOAL. 



suspicion of excess of phosphoric acid, I added a slight ex- 

 cess of alkali to the phosphate of potash, so that its solu- 

 tion turned blue colours green. This phosphate, dried at 

 a red heat, weighed 30 gram. [463 gvs.]. It was powdered 

 and triturated with twice its weight of beech charcoal, which 

 had been red hot just before they were mixed. I put the 

 whole into a small coated porcelain retort, and exposed it 

 for four hoars, in the furnace described in the preceding 

 section, to the same degree of heat as in the preceding ope- 

 ration. The phosphorus flowed by drops into the water of 

 the receiver; and, though 1 extinguished the fire while some 

 p!)osplioric fumes were still evolved, I collected in the re- 

 ceiver and in the adopter, 2*5 gram. [38 grs.] of phospho- 

 rus. In this weight I do not iufclude a portion of this sub- 

 stance, which adhered to the neck of the retort; what was 

 suspended in the water of the receiver, and rendered it yel- 

 low like whey ; or what waS^ combined in the phosphuretted 

 hidrogen gas produced ia"this distillation. If it be consi- 

 dered, that 30 gram, of phosphate of potash contain. by cal- 

 culation about 4-8 gram. [74 grs.] of phosphorus only, there 

 can be no doubt, that this salt was almost wholly or in great 

 part decomposed by the charcoal. 



1?ECT. 3. Decomposition of Phosphate of Soda by Charcoal, 



Phosphate of Fo'" ^^^'^ experiment I employed crystallized phosphate of 

 soda fiecom- soda, with a slight excess of the alkali, according to the 

 coftl ^ ^ ^ common practice of the shops for obtaining regular crystals. 

 By drying at a red heat 100 parts of this salt were reduced 

 to 40*94. I powdered 30 gram, of this phosphate, and mixed 

 with it 60 gram, of beech charcoal, which I made red hot 

 immediately before mixing them. The operation was con- 

 ducted as ia the precedn^g instance, and I collected the 

 same product, namely 2-5 gram, of phosphorus, with the 

 same omissions as before. 



As the phosphates of potash and of soda deprived of their 

 waters of crystallization contain nearly similar quwilities of 

 phoRphoric acid, we may deduce from them the same con- 

 clusions. 

 Why other The decomposition of the phosphate of soda by charcoal 



ch<-m>sts have ^^^ bceu a particular object of inquiry to chemists. It is to 



be 



