In the foregoing process for the conversion of the oxides of nitrogen into nitrous and nitric acid, any of the substances known to chemists as catalytic or contact substances may be empleyod, of which mention has only been made of platinum as a type of the class. Instead of the platinum and tube i, a closed vessel containiog water may be used, which de,composes hyponitrous and nitrous acids, giving rise to nitric acid. Thia principle has been applied in the following ways :—The oxides of nitrogen, as evolved from the liquor in the &composing vessel, as before mentioned, coming in contact with oxygen as already described, are converted into hyponitrous or nitrous acid, which upon being mingled with steam are decomposed into nitric acid and binoxido of nitrog,en, or the introduction of steam may be obviated by using heated air or oxygen in the decomposing vessel, by which means moisture will be furnished from the liquor ; the amount of evaporation thus caused will also prevent an inconvenient increaso in the quantity of mother liquor. The compounds thus formod are than passed into a refrigerating vessel or apparatus, which may be either an earthenware worm surrounded by water, or a series of receivers, such as are ordinarily used for the condensation of nitric acid, and if the atmospheric air or oxygen so supplied has been in slight excess the whole of the gases, or nearly all, will be eoudensed as a nitric acid. It may be remarked here that by forcing in atmospheric air or oxygen gas at any other part of tho apparatus, the same effect in converting tho gaseous oxides of nitrogen into hypenitrous, nitrous, and Dario acids may be obtn tied.
The noxt step was to render tho process continuous instead of intermittent, and this is accomplished by an apparatus of the following nature. The mother liquor is placed in a covered vessel termed a generator, in the top of which is an opening for the insertion of the mother liquor and the withdrawal of the product upon completion of the process, and which may be rendered air-tight by a well-fitting lid. At another opening in the top of the generator a thermometer is flx(sl, to show the temperature of the contents of the generator during the operation. Two funnel pipes, with elongated stems, pass through the top of the generator, and reaching nearly to its bottom, serve to coovey proportionally and by degrees the rnaterials to be decomposed or acted on from feeding vessels which are furnished with stopc,ocks so as to enable the operator to regulate the supply according to the length of time over which it may be wished to extend the operation. Steam or hot water circulates through a pipe for the purpose of heating the liquor in the generator. There is an opening in the top, te which an eduction pipe is adapted to convey away the gases generated during the operation to a receiver, which pipe dips below the surface of the fluid in the receiver, and the receiver is filled up to an overflow pipe at the commencement, whit, any excess escapes into a reservoir, aod so maintains the same amount of pressure throughout the process. A pipe attached to a chlorine generator adtnits a current of chlorine gas, which pipe al-o (lips below the surface of the fluid. Connecting arms eenvey the gases or vapours to a series of condensers, and overflow pipes convey away the condensed fluid from the condensers through a pipe with the necessary openings to allow the overflow pipes to descend to the bottom of the main ; there is a waste pipe or cook situated 2 iu. from the bottom of the main, which dis_ charges its contents into a collecting pan. A pipe passes from the last condenser into the exterior atmosphere, to carry off the waste gases. The whole of the above-described apparatus having been properly arranged and a quantity of mother liquor placed in the generator, and nitric acid and syrup in the usual proportion to such quantity of mother liquor placed separately in the feeding vessels, heat is to be applied, and the temperature of the liquor raised as quickly as possible to 82° (I80° F.) to 91° (200° F.). Streams of nitric acid and syrup are then caused to flow
by turning the stopcocks through the funnel pipes into the liquor in such quantity that the deli very of the whole shall oc,cupy about eighteen hours, at the expiration of which tiane the proes will he completed. The gas or gases arising from the decornposition of the materials so supplied will puss off through the eduction pipe into the receiver, where a stream of chlorine is to be intro duced from the chlorine generator through the pipe, sufficient to convert the whole of the oxides of nitrogen into nitric acid. A portion of the water in the receiver will be decomposed, ita hydrogen combining with the oxide of nitrogen to form nitric acid, while its hydrogen will combine with the chlorine to form hydrochloric acid ; these mixed vapours passing onward into the condensing vessels will there be condensed. The whole of the nitric acid and syrup having been run in, and the liberation of the gases or oxides of nitrogen having ceased, the liquor is drawn off from the generator by means of a syphon, and placed in a convenient vessel to crystallize. Although we have described in the above process the application of a temperature of from 82° to 91° as being that which is preferred, still if it be thought desirable the liquor may be heated even to the point of ebullition without detriment to the success of the process.
As regards the second part of the invention, which relates to the manufacture of salts, it con sists, first, in manufacturing nitrates by means of the oxides of nitrogen and oxygen gas, or atmo spheric air, in conjunction with basic substances, the oxides of nitrogen, however procured, being mixed with atmospheric air or oxygen gas, and made to pass through a chamber or other apparatus containing a metal or metallic oxide, or any alkali or alkaline earth, the presence of which basic substances induces a simultaneous combination of the oxide with oxygen, and the base thus em ployed forms a nitrate ; for example, lime in the state of quicklime, hydrate, or carbonate is placed in a chamber en trays, or in an apparatus similar to the "dry lime purifier" used in gasworks (or a series of them), and a current of the mixed gases passed slowly through them ; and when the gas that is given off from the last vessel is found to contain nitrous acid, the contents, which will be nitrate of lime, should be withdrawn and the vessel replenished. We would here remark that care should be taken to ensure the presence of a sufficient quantity of atmospheric air or oxygen in the vessels, so as to cause the entire conversion of the oxides of nitrogen to the highest degree of oxy genation, and their consequent combination with the basic substance ss nitrate. The following mode of ascertaining this has been found sufficient for the purpose, namely, the absence of any of the oxides of nitrogen, together with the presence of free oxygen in the gas that issues from the last vessel, shows that sufficient oxygen has been furnished ; on the contrary, should red fumes make their appearance upon allowing a portion of the gases to escape into the atmosphere, and which gases were previously colourless, it is a proof that there has been a deficiency of oxygen, and consequently more atmospheric air or oxygen gas must he passed into the apparatus. When a metal is employed, in the place of lime as above-mentioned, it is preferable to reduce it previously to small particles by granulation, or otherwise, so as to expose a larger surface to the action of the mixed gases.