1. _Protoxide._ There are two methods of obtaining the constitution of this oxide. The first is by dissolving a certain weight of tin filings in muriatic acid, precipitating by lime water or carbonated alkalies and drying the oxide in a moderate heat; this is liable to some uncertainty; the precipitate being a _hydrate_, requires to be exposed to heat to expel the water; but if the heat approaches to red, the oxide takes fire and is converted into the deutoxide. The second method is to dissolve tin in muriatic acid and carefully collect the hydrogen gas evolved; this was first done by Mr. Cavendish, with his usual accuracy, and published in 1766; he found 1 oz. of tin yield 202 oz. measures of hydrogen gas. I have frequently tried this experiment and always found a proportional quantity, or very nearly 200 measures for each grain of tin. This mode of investigation appears to me unexceptionable. Now 200 hydrogen unite to 100 oxygen, and 100 grain measures of oxygen = .134 grain in weight; hence if .134 oxy. ∶ 1 tin ∷ 7 oxy. ∶ 52 nearly for the weight of an atom of tin, on the presumption this is the protoxide. 2. _Deutoxide._ This may be obtained by heating tin till it takes fire, and the produce of the combustion is the oxide required; but to ascertain the proportions of tin and oxygen two other methods are preferable; the one is to treat tin with nitric acid of the sp. gr. 1.2 to 1.4; a violent effervescence and great heat ensue and the tin is converted into a white powder. This being dried in 100° gives about 160 grains for 100 of tin. It consists of the deutoxide united to a little acid and water; these two may be driven off by a low red heat, and 127 grains of the deutoxide remain in the state of a white powder. The other method is to treat a solution of the protoxide of tin with oxymuriate of lime till it is saturated; this will be found when 59 grains of the protoxide have acquired 7 grains of oxygen, or 113½ grains of the deutoxide have acquired 13½ grains of oxygen, which corroborates the result by the 1st method. This oxide containing just twice as much oxygen as the former, may justly be considered as the deutoxide. No higher oxide of tin has been obtained. The two oxides, though both white when precipitated, may be distinguished from their different appearances; the first is _curdy_, the second, _gelatinous_. It may be proper to subjoin authorities for these oxides: Tin Protoxide Deutoxide Cavendish, from the hydrogen 100 113.5 -------- Proust (Journ. de Physique 59-341) 100 115 127½.128[10] Gay Lussac (Annal. de Chimie 80-170) 100 113.5 127.2[11] Berzelius (Annal. de Chim. 87-55) 100 113.6 127.2[12] My own, as above 100 113.4 127