THE ANALYST. 41 A NEW TEST FOR LEAD. BY A. WYNTER BLYTH, M.R.C.S. A SOLUTION of cochineal is prepared by boiling the ordinary commercial cochineal in water, filtering, and then adding suflicient strong alcohol to ensure its preservation from mould. A few drops of this solution added to a colourless neutral or alkaline solution containing dissolved lead, strikes a deep mauve blue to a red with a faint blue tinge, according to the amount of lead present. The test will distinctly indicate a tenth of a grain of lead per gallon in ordinary drinking water, and by comparison with a solution free from lead, much smaller quantities are indicated. In searching for traces of lead in water, it is convenieut to take two porcelain dishes ; into the one place 100 c.cs. of the water to be examined and into the other, a solution of carbonate of lime in carbonic acid water, known to be lead free, and approximatively of the same hardness, as the water to be examined, then add to each an equal bulk of the colouring matter in quantity sufficient to distinctly tinge the water ; the colours may now be compared ; the slighest blue tint will be either due to lead or copper ; for copper in very dilute solutions gives a similar tint, but in solutions of 1 to 1,000 or stronger the hue is so different as to differentiate the two metals. The method is within certain limits applicable for quantitative purposee on the usual colorimetric principles.As a qualitative test, it is superior to hydric sulphide and more convenient. DISCUSSION. DR. STEVENSON inquired if varying the amount of alkalinity in the water, or the presence of considerable quantities of carbonates, had any effect. Mr. BLYTH said that of course they altered the hue, but the blue was still very de- cided. He had tried a11 kinds of saltg but as it was anew test, he would be a bold man to say that it was really confined to these, although, as far as he knew, it was peculiar to lead and to copper, with the limitations he had mentioned. The tests were confirmed by other reactionfir.