44 Dr. R. D. Thomson on the History [Jan. 



being largely diluted re-assumed its blue tint. As from the 

 appearance of the colours in the solution, it was evident that 

 some of the acid had parted with a portion of its oxygen, 

 and been reduced to the state of oxide, it was necessary to 

 render the whole of a homogeneous nature. For this pur- 

 pose a quantity of oxalic acid was added to the liquid, and 

 to ensure the total conversion of acid into oxide, a current 

 of sulphuretted hydrogen was passed through it. The 

 solution became muddy and a dark precipitate appeared, 

 which was separated by filtration, and when heated was 

 completely volatilized, and was obviously sulphur. The 

 solution possessed now a rich blue colour. It was concen- 

 trated on the sand bath, in order to drive off the excess of 

 sulphuretted hydrogen. Nitrate of lead afforded no pre- 

 cipitate, indicating the absence of sulphur and phosphoric 

 acid. An excess of carbonate of soda was then added, 

 which precipitated the hydrous oxide of vanadium, in the 

 form of a bulky greenish brown precipitate, becoming 

 black by exposure to heat. It was thrown on a filter and 

 washed with hot water. After exposure to a red heat, it 

 weighed 21*39 grains. According to the numbers which 

 Berzelius has attached to the oxides of vanadium, we have, 

 in order to arrive at the quantity of acid which is equiva- 

 lent to this portion of oxide, the following proportion : — 

 10-5 : 11-5:: 21-39 : 23-436 = vanadic acid. 

 The results of the analysis therefore are : — 



Chlorine ... -734 2-446 



Protoxide of lead 22-164 73*880 



Vanadic acid . . 7-031 23-436 



Insoluble matter . -048 0-160 



29-978 99-923. 

 If we view the acids as forming subsalts with the bases, 

 with which the numbers nearly agree, the composition of 

 the mineral will be 



100-000 



