Such a review of the subject would, moreover, appear to be essentially necessary at the present period, since the evidence, lately delivered on an extraordinary trial,[240] has, to a certain extent, very unjustly shaken the public confidence in the tests of chemistry. We shall therefore proceed to consider the processes which are calculated to lead to the detection of _Arsenic_, in relation to the different circumstances under which it may be presented for investigation, viz. 1, In a solid form; 2, In the simple state of solution; and 3, In the state of combination with various alimentary substances. 1. _The Arsenic is in a solid form._ This is the most simple case which can occur, and the experiments by which its presence is to be demonstrated, will constitute the basis of the inquiry, which we shall be hereafter called upon to institute, for the detection of the same substance under other circumstances of mixture and combination. The order of succession to be observed in the different experiments which we are about to describe, must, in a great measure, be regulated by the quantity of the material to be submitted to examination. Should it be small, it will be prudent to reserve the process of metallization, by which a considerable loss must necessarily arise, until we have submitted it to the various re-agents which are calculated to afford indications of its nature. If, on the contrary, the quantity of the substance exceed two or three grains, it will be adviseable to proceed in its examination by the following processes, reserving a portion for future analysis.