some of the crystals in water, saturating the solution with ammonia, and then treating it with the oxalate of that alkali, which, if lime be present, will immediately separate it in a palpable form. The juices of many other fruits besides the lemon and lime, will furnish the citric acid in abundance, and may be obtained from them by a similar process; e. g. VACCINIUM OXYCOCCUS, the _Cranberry_; PRUNUS PADUS, the _Bird’s Cherry_; DULCAMARA SOLANUM, the berry of the _Nightshade_; CYNOSBATUS, vel ROSA CANINA, the hep or fruit of the _Wild Briar_. There are many plants whose juices contain combinations of the _Citric_ and _Malic_ acids in considerable abundance, such as FRAGARIA VESCA, the _Wood Strawberry_, and the common _Raspberry_; RIBES RUBRUM the _Red Gooseberry_; VACCINIUM MYRTILLUS, the _Bilberry_; CRATÆGUS ARIA, the _Hawthorn_; PRUNUS CERASUS, the _Black Cherry_, &c. This fact is interesting, since the juices of such fruits have been long known to possess the property of dissolving the _tartareous_ incrustations on the teeth. ACIDUM HYDRO-CYANICUM. _Hydro-cyanic Acid._ _Prussic Acid._ This peculiar acid exists in a great variety of native combinations in the vegetable kingdom,[341] and imparts to them certain properties which have been long known, and esteemed in medicine. It is, however, only lately, that it has been administered in its simple but diluted form. As few practitioners will choose to prepare the acid, it seems unnecessary in the present work to dwell upon the merits of the different processes which have been proposed for its preparation; for a full account of them, as well as for other details of importance, the practitioner is advised to consult a work by Dr. Granville, entitled “_An Historical and Practical Treatise on the use of Prussic Acid. Second Edition. London, 1820._”