and on the Crystalline Solid formed in that Process. 1 1 9 



sustain loss by allowing the gravity of house-acid to become 

 too high, say to T60. The Experiment (6) will show that; 

 and if the gravity is allowed to reach that degree, the solid, as 

 it falls into it, will undergo but partial decomposition. The 

 nitrous acid will be retained ; and as there is little absorption 

 of sulphurous acid gas, the nitrous acid is little acted upon ; it is 

 drawn off with the oil of vitriol, and does not wholly quit it un- 

 less the oil of vitriol is combined with a base. When the acid is 

 drawn from the lead-house at sp. gr. 1*25 to 1*30, it gives 

 off copious fumes of sulphurous acid, because enough of the 

 solid has not been precipitated into it to convert the absorbed 

 sulphurous into sulphuric acid; nor is it probable that suf- 

 ficient nitrous gas can be absorbed, as such, from the chamber 

 already filled with sulphurous gas, to effect; such a change : 

 it can be effected only by having the white solid put into it. 

 If acid is drawn from the lead-house from sp. gr. 1*35 to 

 1*40, then it is filled with deutoxide of azote and with nitrous 

 vapour; we perceive this by its smell when the acid is boiled. 

 When acid is drawn from the house at sp. gr. 1*60 and up- 

 wards, very little decomposition of the solid having taken 

 place, we then see the red vapour fill the retort neck, when 

 the acid is concentrated ; but we do not smell it when the acid 

 is boiled in the leaden kettle; it requires probably a higher 

 degree of heat than that of the kettle, to drive off the nitrous 

 acid; it is not all driven off even by concentration. 



It is evident too from the effects of cold in Experiments (3 

 and 6) that the hyponitrous acid is not decomposed at low tem- 

 peratures, or when decomposed, the gas resulting is retained by 

 the liquid. Hence, in very cold weather, part of the crystal- 

 line solid is collected on the walls of the lead- house; that 

 which falls into the liquid is less easily decomposed, and when 

 decomposed, its gases are more readily retained. This is the 

 reason why the manufacturer suffers ; his product of acid is less, 

 because the sulphurous acid gas, not having nitrous vapour 

 to mix with and precipitate it, escapes dry and almost invisi- 

 ble. The great truths are well known, that in the manufac- 

 ture of oil of vitriol, loss always occurs when fresh water only 

 is used in the lead-house, or when the weather is very cold, or 

 when the gravity of the house-acid is too high. The best 

 results are obtained by an even temperature of 50° Fahr. 

 Steam cannot be used to obviate the inconveniences of cold, 

 unless applied to heat the acid liquid in the house ; for unless 

 the temperature of this is kept up, the mere warming of the 

 walls would be immaterial. Too much steam injected into the 

 chamber lessens the product of acid, it acts like fresh water, 

 rendering the nitrous vapour useless. 



