10. _Phosphorus_ is a soft pale yellow substance which readily takes fire in the air, and gives off, while burning, a dense white smoke. The white fumes which form this smoke are a compound of phosphorus with oxygen obtained from the air, and are called _phosphoric acid_. In the ash of plants the phosphorus is found in the state of phosphoric acid, though it probably does not all exist in the living plant in that state. _Phosphoric acid_ forms _phosphates_ with potash, soda, lime, and magnesia. When bones are burned, a large quantity of a white earth remains (bone-earth), which is a _phosphate of lime_, consisting of lime and phosphoric acid. Phosphate of lime is generally present in the ash of plants; phosphate of magnesia is contained most abundantly in the ash of wheat and other varieties of grain. 11. _Chlorine._—This is a very suffocating gas, which gives its peculiar smell to chloride of lime, and is used for bleaching and disinfecting. It is readily obtained by pouring muriatic acid (spirit of salt) on the black oxide of manganese of the shops. In combination with the metallic bases of potash, soda, lime, and magnesia, it forms the _chlorides_ of potassium, sodium (common salt), calcium and magnesium,[7] and in one or other of these states it generally enters into the roots of plants, and exists in their ash. [7] Potash, soda, lime, and magnesia, are compounds of the metals here named with oxygen. It is a very striking fact, that the suffocating gas chlorine, when combined with sodium, a metal which takes fire when placed upon water, should form the agreeable and necessary condiment, _common salt_. Such are the inorganic substances usually found mixed or combined together in the ash of plants. It has already been observed, that the quantity of ash left by a given weight of vegetable matter varies with a great many conditions. This fact deserves a more attentive consideration. SECTION II.—OF THE DIFFERENCE IN THE QUANTITY OF ASH. 1. The quantity of ash yielded by _different plants_ is unlike. Thus 1000 lbs. of Wheat leave 12 lbs. Oats 26 lbs. Turnips 8 lbs. Red Clover 16 lbs. Rye Grass 17 lbs. Barley 25 lbs. Potatoes 8 lbs. Carrots 7 lbs. White Clover 17 lbs.