of Molybdenum and some of its Compounds. 535 



Experiment with Neutral Molybdate of Potash. 



Calcined neutral molybdate of potash was heated in a cur- 

 rent of dry air in a counterpoised reduction-tube, weighed after 

 cooling, and then connected with a sulphuretted hydrogen 

 apparatus. The dry sulphuretted hydrogen acted instantly, 

 and with considerable evolution of heat, upon the potash salt, 

 water was formed, and the salt assumed an orange-red and 

 gradually a dark reddish-brown colour. After some time the 

 reaction ceased, the bulb became cold, and it was now gently 

 heated with a small lamp; a considerable disengagement of 

 water immediately ensued, and the sulphuretted hydrogen was 

 so rapidly absorbed that not a bubble passed through the 

 apparatus. It is necessary to raise the temperature gradually 

 towards the end, that the entire mass may be incandescent: 

 a portion of the contents fuses. At the commencement the 

 action of the sulphuretted hydrogen is very energetic, but it 

 soon decreases and proceeds very slowly, so that much time 

 elapses before no further formation of water is perceptible. 

 On attaining this point the bulb was allowed gradually to 

 cool, and here a peculiar phaenomenon occurred, — as soon as 

 the bulb had acquired a certain lower temperature, the whole 

 of the sulphuretted hydrogen was absorbed by the mixed 

 sulphurets : not a single bubble past through for some time. 

 This condensation of the sulphuretted hydrogen we first ob- 

 served in making this experiment ; it is probable, however, 

 that the differences in the weighings in the former experiment 

 were owing to the same cause. 



As this condensation must give rise to an error, we ex- 

 pelled the sulphuretted hydrogen by a current of dry carbonic 

 acid, keeping the bulb at a gentle heat ; but although we 

 passed carbonic acid through the tube for an hour, sul- 

 phuretted hydrogen was constantly given off, but not a trace 

 of sulphurous acid was perceptible. As this led to our object, 

 we expelled the sulphuretted hydrogen, immediately after the 

 cooling, by dry air, and then weighed it as quickly as possible. 

 At the end of the experiment the contents of the bulb were fused 

 partly to a reddish-brown mass, which had acted very much 

 upon the glass, and a portion had formed a mass with a plombi- 

 ferous hue. The contents were now treated with water, which 

 gave an orange-red solution, while sulphuret of molybdenum, 

 Mo S 2 , separated ; it was collected upon a filter, washed, dried 

 at 212°, and its weight determined. On evaporating the 

 filtered solution, and slow crystallization, we obtained the 

 beautiful compound described by Berzelius under the name of 

 sulphomolybdate of potassium ; but besides these crystals the 



