OF ASCERTAINING THE PRESENCE OF DIFFERENT METALS. 149 
in the state of foil, or of thin sheet. The platina was in some cases a small 
crucible, or a spatula having a spoon at the end of it, but more frequently 
platina foil was employed. The foil was about two inches long, and two thirds 
of an inch wide. The zinc foil varied from about one third to one eighth of the 
size of the platina foil. The size and thickness of either metal may vary inde- 
finitely, without materially altering the results. This simple arrangement is 
most easily applied to the decomposition of a great number of metallic com- 
pounds. It is only necessary to mix a drop or two of acid with a little of such 
compounds, whether solid or fluid, and apply the zinc foil, when the platina 
will be soon coated with the reduced metal. Solutions of many metallic salts 
do not require the addition of acid. I may remark that the small slips of 
platina and zinc foil are very convenient for many experiments on metallic 
poisons ; as where the object is to ascertain the presence of arsenic or mer- 
cury, in a fluid in which it may exist in considerable quantity ; or to determine 
whether any powder contain either of those metals in combination. One slip 
of platina will answer for an indefinite number of such experiments ; one slip 
of zinc, too, may be employed for many experiments. It is only necessary 
either to dip the end, after being used, into a little water, and wipe it, or to cut 
the mere point off at once. The platina spatula with a spoon at the end of it, 
is well adapted for concentrating, or boiling nearly to dryness, fluids which may 
contain metallic poisons, but in such minute quantity, as to render concen- 
tration indispensably necessary to the success of the electro-chemical method 
of detecting them. The small platina crucible is a necessary appendage to the 
apparatus, in cases, where from previous trials by the platina foil, or spoon, and 
zinc, the existence of a metallic poison has been proved in a fluid or solid, in 
order to collect it in sufficient quantity, and exhibit it in a separate state. 
3 . Experimental proofs of the efficacy of the Electro-chemical method to detect 
different metals, and especially metallic poisons. 
Solutions of gold, silver, mercury, copper, tin, lead, &c. are not decomposed, 
as is well known, by platina ; but if a drop of each of those metallic salts, con- 
taining excess of acid, be severally placed on a surface of platina, and a slip 
of zinc brought in contact with both, each salt will be decomposed, and the 
