Here I will add only that the domestic gum of cherry and plum trees is good for preparing stones some years and worthless in others, when it cannot be dissolved in water. In possessing the properties for preparing stone, the juice of many plants and fruits, sugar, and most mucous materials of the vegetable and animal kingdom, such as white of egg, approach gum arabic more or less. The latter, however, is to be preferred because of its reliability. IV CONCERNING PARTIAL PREPARATION Here I impart my experiences in regard to an astonishing phenomenon that occurs often in lithography and gives much trouble, especially to beginners. It is the so-called imperfect or semi-preparation, wherein the stone betrays a strong inclination to take color, and still will not do it or will do it only partially. (_a_) If a cleanly ground stone is marked with chemical ink, etched, and prepared, the marked places will take the printing-color and produce impressions. If, after the stone is inked, one rubs strongly with the wetted finger, the color can be wiped from the design, especially if it has not been on the stone long and has been standing in a damp place. A place whence the color thus has been removed does not take it readily when the inking-roller is applied again; and the reluctance is the greater in proportion to the length and violence of the rubbing and the toughness of the printing-color. The stone shows clearly the traces of the penetrating fat; indeed, if the stone is rubbed with a wet linen rag that is inky from previous use, the design will reappear in black. But as soon as the roller is used, instead of inking these places, it takes the color off; and whatever means may be tried to make the defective places receptive again to color, it remains difficult, often impossible. What has happened is that the wet rubbing has cleansed the surface of the stone of all its fat and at the same time has polished it and made it slippery. It is a sort of preparation; and though the fat of the ink has penetrated into the interior of the stone, the accidental preparation still offers an obstacle which prevents the printing-ink from adhering to the fat in those places. As I will show, these places can be prepared again thoroughly. (_b_) Another case is when the design is too weak, and has been attacked by the etching-fluid too powerfully, though without being destroyed. Here the printing-color usually is removed by the ink-roller, even though it adheres pretty well when being wiped. (_c_) A third kind of imperfect preparation is when a stone inclines to take color or smut on prepared places. This happens sometimes in part, sometimes over the whole surface, which latter effect is described by saying that the stone has acquired a tone. The cause of this phenomenon may be one of many. It is either due to the appearance of a fat that has been in the stone, or to the fact that unskilled manipulation has destroyed the preparation partially.