"_The oxalate of lime, or mulberry calculus_, is generally of a very dark brown colour, approaching to black. Its surface is very rough and tuberculated (hence the epithet of _mulberry_.) It is usually hard, and when cut through exhibits an imperfectly laminated texture. This species of calculus seldom surpasses the medium size, and is rather common. There is a variety of it remarkably smooth, and pale coloured. These are always of small size; and from their colour and general appearance, have been termed the _hempseed_ calculus.--_Chemical characters._ Before the blow-pipe, this species of calculus expands into a kind of white efflorescence, which, when moistened and brought into contact with turmeric paper, stains it red. This white alkaline substance is the caustic lime deprived of its oxalic acid." "_The triple phosphate of magnesia-and-ammonia calculus_ is always nearly white; its surface is commonly uneven, and covered with minute shining crystals. Its texture is not laminated, and it is easily broken and reduced to powder. In some rare instances, however, it is hard and compact, and when broken exhibits a crystallized texture, and is more or less transparent. Calculi composed entirely of the triple phosphate of magnesia-and-ammonia are rare; but specimens, in which this salt constitutes the predominant ingredient, are by no means uncommon.--_Chemical characters._ Before the heat of the blow-pipe, this calculus gives off the odour of ammonia, and at length melts with difficulty. It also gives off ammonia, when treated with caustic potash. It is much more soluble than the preceding species in dilute acids, from which it is again readily precipitated by ammonia in its original crystallized form.