_Chlorine_ is by no means an invariable constituent of the ash, although it is generally present, and sometimes in considerable quantity. It is most abundant when the proportion of soda is large, and exists in the ash principally in combination with that base as common salt. The relation between these two elements may be traced more or less distinctly throughout the whole table of analyses, and conspicuously in that of mangold-wurzel, where the common salt amounts to almost exactly one-half of the whole mineral matter. The analyses of the cultivated and uncultivated asparagus also show that a diminution in the soda is accompanied by a reduction in the proportion of chlorine. _Sulphuric Acid_ is an essential constituent of the ash. But it is to be observed that it is in some instances entirely, and in all partially, a product of the combustion to which the plant has been submitted in order to obtain the ash. It is partly derived from the sulphur contained in the albuminous compounds, which is oxidised and converted into sulphuric acid during the process of burning the organic matter, and remains in the ash. The quantity of sulphuric acid found in the ash is, however, no criterion of that existing in the plant, for a considerable quantity of it escapes during burning. The extent to which this occurs in particular instances is well illustrated by reference to the case of white mustard, which yields an ash containing only 2.19 of sulphuric acid, equivalent to 0.9 of sulphur; and if calculated on the seed itself, this will amount to no more than 0.039 per cent, while experiments made in another manner prove it to contain about thirty times as much, or more than 1 per cent. For the purpose of determining the total quantity of sulphur which the plants contain in their natural state, it is necessary to oxidise them by means of nitric acid; and from such experiments the following table, showing the _total_ amount of sulphur contained in 100 parts of different plants, dried at 212 deg., has been constructed:-- Poa palustris 0.165 Lolium perenne 0.310 Italian Ryegrass 0.329 Trifolium pratense 0.107 repens 0.099 Lucerne 0.336 Vetch 0.178 Potato tuber 0.082 tops 0.206 Carrot, root 0.092 tops 0.745 Mangold-Wurzel, root 0.058 tops 0.502 Swede, root 0.435 tops 0.458 Rape 0.448