Continue the distillation, increasing the fire a little when you observe the drops to follow each other but slowly, so that above two thirds of a minute passes between them; and, in order to let out the redundant vapours, open the small hole in the receiver from time to time. Towards the end of the operation raise the fire so as to make the retort red. When you find that, even when the retort is red-hot, nothing more comes over, unlute the receiver, and without delay pour the liquor it contains into a crystal bottle, and close it with a crystal stopple ground in its neck with emery. This liquor will be of a reddish yellow colour, smoking exceedingly, and the bottle containing it will be constantly filled with red fumes like those observed in the receiver. _OBSERVATIONS._ The Vitriolic Acid having a greater affinity with Fixed Alkalis than with any other substance, the Phlogiston excepted, and being in the Vitriol united with a ferruginous basis, will naturally quit that basis to join with the Fixed Alkali of the Nitre; the Acid whereof being weaker than the Vitriolic, as we have already observed on several occasions, must needs be thereby expelled from its basis. The Nitre therefore is decomposed by the Vitriol, and its Acid being set at liberty, is carried up by the force of the fire. Indeed the Nitrous Acid, being thus separated from its alkaline basis, might be expected to combine with the ferruginous basis of the Vitriol: but as it has, like all other Acids, much less affinity with Metallic substances than with Alkalis, even a moderate degree of fire is sufficient to separate it from them. Moreover, this Acid hath either no effect, or very little, upon iron that has lost much of its Phlogiston by contracting an union with any Acid; which is the case of the ferruginous basis of Vitriol. By the process here delivered a very strong, perfectly dephlegmated, and vastly smoking Spirit of Nitre is obtained. If the precautions of drying the Nitre and calcining the Vitriol be neglected, the Acid that comes over, greedily attracting the water contained in these salts, will be very aqueous, will not smoke, and will be almost colourless, with a very slight tinge of lemon. The fumes of highly concentrated Spirit of Nitre, such as that obtained by the above process, are light, corrosive, and very dangerous to the lungs; being no other than the most dephlegmated part of the Nitrous Acid. The person therefore who unlutes the vessels, or pours the liquor out of the receiver into the bottle, ought with the greatest caution to avoid drawing them in with his breath; and for that reason ought to place himself so that a current of air, either natural or artificial, may carry them off another way. It is also necessary that care be taken, during the operation, to give the vapours a little vent every now and then, by opening the small hole in the recipient; for they are so elastic, that, if too closely confined, they will burst the vessels.