add slowly about 5 cc. in excess of that amount, with constant stirring.  Heat the solutions cautiously to boiling, stirring occasionally, and continue the heating and stirring until the precipitates settle promptly, leaving a nearly clear supernatant liquid (Note 3).  This heating should not take place in direct sunlight (Note 4).  The beaker should be covered with a watch-glass, and both boiling and stirring so regulated as to preclude any possibility of loss of material.  Add to the clear liquid one or two drops of silver nitrate solution, to make sure that an excess of the reagent is present.  If a precipitate, or cloudiness, appears as the drops fall into the solution, heat again, and stir until the whole precipitate has coagulated.  The solution is then ready for filtration.

Prepare a Gooch filter as follows:  Fold over the top of a Gooch funnel (Fig. 2) a piece of rubber-band tubing, such as is known as “bill-tie” tubing, and fit into the mouth of the funnel a perforated porcelain crucible (Gooch crucible), making sure that when the crucible is gently forced into the mouth of the funnel an airtight joint results.  (A small 1 or 1-1/4-inch glass funnel may be used, in which case the rubber tubing is stretched over the top of the funnel and then drawn up over the side of the crucible until an air-tight joint is secured.)

[Illustration:  Fig. 2]

Fit the funnel into the stopper of a filter bottle, and connect the filter bottle with the suction pump.  Suspend some finely divided asbestos, which has been washed with acid, in 20 to 30 cc. of water (Note 1); allow this to settle, pour off the very fine particles, and then pour some of the mixture cautiously into the crucible until an even felt of asbestos, not over 1/32 inch in thickness, is formed.  A gentle suction must be applied while preparing this felt.  Wash the felt thoroughly by passing through it distilled water until all fine or loose particles are removed, increasing the suction at the last until no more water can be drawn out of it; place on top of the felt the small, perforated porcelain disc and hold it in place by pouring a very thin layer of asbestos over it, washing the whole carefully; then place the crucible in a small beaker, and place both in a drying closet at 100-110 deg.C. for thirty to forty minutes.  Cool the crucible in a desiccator, and weigh.  Heat again for twenty to thirty minutes, cool, and again weigh, repeating this until the weight is constant within 0.0003 gram.  The filter is then ready for use.

Place the crucible in the funnel, and apply a gentle suction, !after which! the solution to be filtered may be poured in without disturbing the asbestos felt.  When pouring liquid onto a Gooch filter hold the stirring-rod at first well down in the crucible, so that the liquid does not fall with any force upon the asbestos, and afterward keep the crucible will filled with the solution.

Pour the liquid above the silver chloride slowly onto the filter, leaving the precipitate in the beaker as far as possible.  Wash the precipitate twice by decantation with warm water; then transfer it to the filter with the aid of a stirring-rod with a rubber tip and a stream from the wash-bottle.