On the supposition that the nitrogen compound exists as nitrous acid, the 200 parts sulphurous acid will take 50 —1.129 = parts of oxygen from the air, whilst the parts of nitrous acid only contain part of oxygen. Then the nitrous acid enables the volume of oxygen taken from the air to be 48.871 = times as great as its own volume of oxygen. 1.695 Consumption of Nitre, or Nitric Acid.—When the consumption of sulphur takes place in the proportion we have indicated, and the process is well conducted, the amount of nitre necessary per 100 parts of sulphur will be about 6, or 3.812 per c,ent. of anhydrous nitric acid. If the sulphur consumption be increased, or the conduct of the work be irregular, this percentage may easily be increased to 7•5.
Market fluctuatione and other causes sometimes necessitate an increased prodnction, or that the chambers be " forced." But it is never advibable to exceed the limits mentioned above, because, beyond a certain limit, the increased consumption of nitre, which bears a direct propor tion to the increased product of acid, will have the effect of creating a rapid corrosion of the lead vrithont any corresponding augmented yield of acid. On the other hand, it is not good to let the coneumption and product fall too low, because the process then becomes retarded in several ways, especially through the cooling of the apparatus.
When the nitrogen compounds are produced by the decomposition of nitre with eulphuric acid in the kiln, it is essential to take care that all the nitrogenone gas be liberated. To ensure this there must be an excess of acid. Generally the proportion is 2 equive. acid for 1 equiv. nitre, by which the alkali is formed into a bisulphate. So large a proportion of acid is not absolutely necessary, however, for all the nitro will be decomposed by 11 part of acid when thc right temperature is maintained. Hence 1 equiv. nitre requires •72 equiv. monohydrated sulphuric acid, or 1.12 equiv. tetrahydrate acid, or at 1•55 sp. gr., which is the strength at which it is commonly used, as it may then be drawn direct from the chambers. With this proportion of tho base will be made into eimple eulphate and f will be bisulphate. Nitre 1 part gives theoretically mixed eulphate of soda • 95 part. This corresponds pretty well with the practical result, as 100 parts nitre give 90-93 parts. Tho difference is owing to mechanical loss.
Commercial nitre nearly always contains u quantity of common salt. This, as well ae the moisture, should always be estimated, and a corresponding increase of nitre be used. The salt muet always bo ascertained, which may be eabily done by a titrated eolution of silver. The beet brande of nitre contain less than f per cent. of salt ; often 2-3 per cent. is met with, and eometimes the article offered in the market is so impure or adulterated as to consiet of 30 per cent. of salt. Nitre containing much more than 3 per cent. must he purified before use by reerystallization, because the chlorine which is otherwise formed attacks the lead of the last chamber when present in large quantities.
In the neighbourhood of alum works, it is eornetimes possible to get nitrate of potash instead of nitrate of soda. 01' this an increased proportion must be used, 1 part of nitre being equal to about 1•19 part saltpetre.
When great care is exercised in passing the gases from the last chamber through a Gay-Lusaac absorber, one half of the nitre consumed may be recovered, thus reducing the percentage by weight from 6 to 3.
Three parts of nitre equal 1. 34 part nitrous acid, and CIS wo have said, sulphuric acid at 150° Tw. takes up 3f per cent. by weight of nitrous acid. Therefore 38.29 parts of sulphuric acid at 150° Tw. are necessary for the recovery of 1•34 part nitrous acid, or 3 per cent. on the sulphur burnt. Often, however, this acid only reaches 112° Tw., though it appears highly probable that the extra cost of concentration to 170° Tw. would be repaid.
The Make of Acid.—When the chamber system is well arranged, the steam accurately adjusted, and the working regularly managed, only about 3 per cent. of the acid which can be made theoretically is lost. From 100 parts of eulphnr are obtained 297 parts monohydrated acid instead of 306f, the possible maximum. These 297 parts exist in the chambers, however, in a weak state, viz. as 460.65 parts of tetrahydmted acid, or at 1.550 sp. gr., with slight modifications, being some times made little stronger, sometimes weaker. These 460.65 parts tetrahydrated acid = 319.35 parts of acid at 1.845 sp. gr. containing 93 per cent. of monohydrated acid.
According to the figuree we have given above, the daily coneumption of these chambers will be about 9f cwt. of sulphur, and 88f lb. of nitric acid at 68° Tw. =- 8•24 per cent. by weight of the sulphur, and the produotion will be about 44 cwt. of sulphuric acid at 150° Tw. or 30f cwt. at 170° Tw.
When the nitrogen compounds are not derived from nitric acid, but from nitre and sulphuric acid in the kilns, 64 lb. of nitrate of soda (or 6 per cent. by weight of the sulphur) and 72 lb. sulphnric acid at 112° Tw. will he required ; and about 58 lb. of sulphate of soda, of which is as bisulphate, will be formed as a bye.product.
By.theroughly good management of the Gay-Lussac process, one half of these nitrogen compounds ean be saved. The daily consumption will then he reduced to 44 lb. of nitric acid at 68° Tw. = 4•12 por cent. of the weight of sulphur, or to 32 lb. of nitre (3 per cent.) and 36 lb. of sulphuric acid at 112° Tw. On the other hand, 29 lb. less sulphate of soda is produced. The operation needs, how ever, 410 lb. daily of aulphuric acid at 150° Tw.
For raising tho neceesary steam about 5f cwt. of good coal will be needed. When, however a much larger chamber system is supplied from one boiler, the consumption of fuel will not be proportionally increased.
It is hardly necessary to state that the raw materials are always sold upon the basis of the proportion of useful matter which they contain.