QUANTITATIVE ANALYSIS 503 Method. Weighing the Sample. Remove the cup A from the hold-ing-tube B, using a clean cloth and avoiding any contact of A with the hands, place it on the carrier D on the balance pan, and weigh it approximately (i.e., to the nearest mg.). Then remove it from the pan, hold it upright in the cloth, and place ca. 25 mg. of the powdered compound under analysis in the cup: this transfer should be carried out with a micro-spatula in several separate operations, and the total amount must not exceed the limits of 20-30 mg. Then tap the cup gently with the spatula to settle the sample well down into the cup, and carefully remove with a clean cloth any solid still adhering to the outside or to the rim of the cup. Replace the cup on the carrier on the balance pan and weigh it carefully. If the weight proves to be outside the above limits, the compound must be added or removed before noting the weight. Now refit the cup A carefully into the holding-tube B, and insert
This is the end of the preview. Sign up
access the rest of the document.