into a test tube resting in a beaker of cold water. The test tube will serve as a condenser.

b. Warm the flask gradually over the wire gauze. Result? Color of fumes? Keep the end of the delivery tube out of the liquid which condenses in the test tube.

When no more liquid distills over, remove the delivery tube. Only then remove the flame.

The liquid collected is nitric acid. Complete the equation,

KNO3+H2SO, KHSO4+?

What is the color of the acid?

c. Let the flask cool thoroughly. Result? Name the crystalline product. Finally, add water and pour the resulting solution into the sink.

d. Add 1 c.c. of the nitric acid you have made to 1 c.c. of water, and test the action of a drop (use the glass rod) upon litmus. Result?

Into your diluted acid put a piece of white woolen yarn, and warm gently. Remove the yarn. How has it changed?

To 1 c.c. of your dilute acid add a few drops of indige solution. Result?

e. What color does your undiluted acid give to the skin? Will ammonium hydroxide remove the stain?

f. Treat about 2 c.c. of ferrous ammonium sulphate or of ferrous sulphate in a test tube with 15 c.c. water and shake vigorously. Take 5 c.c. of this solution in a test tube, add two drops of dilute nitric acid, incline the tube at an angle of about forty-five degrees, and pour about 3 c.c. concentrated sulphuric acid down the side of

the tube. Describe what takes place where the concentrated acid, which is below, meets the solution.

g. Repeat f, using a solution of potassium nitrate instead of nitric acid. Result? Repeat again with cupric nitrate instead of the acid. Result?

h. If the test just tried is a general one for all nitrates, how would you proceed to test a solution for the presence of a nitrate or nitric acid?

EXPERIMENT XXXV.

NITRITES.

Iron dish, stout iron wire, beaker, test tubes. Potassium nitrate, lead, filter paper, dilute sul

a. Melt together in a shallow iron dish 10 grams potassium nitrate, KNO,, with about 20 grams of lead. Keep the mixture at red heat, and stir twenty minutes with a stout iron wire or a nail held in iron tongs.

b. When the mass is cool add 20 c.c. water, heat to boiling for a few minutes, take out the unused lead, and then filter.

The residue on the filter is lead oxide, PbO. Its color? The filtrate contains potassium nitrite, KNO2, and unchanged nitrate. The reaction is a reduction of potassium nitrate by lead, as is shown in the equation,

KNO3+Pb-→→→→KNO2+PbO.

c. Treat the solution of potassium nitrite from b with dilute sulphuric acid. Result? Treat some potas

sium nitrate solution in a test tube with dilute sulphuric acid, and compare results.

d. The brown gas is nitrogen trioxide, N2O3, formed as shown by the equations,

Apparatus. Test tubes, doubly bent delivery tube.
Material.-Powdered lead nitrate, Pb(NO3)2.

a. Heat 5 grams powdered lead nitrate carefully in a test tube (use a holder), keeping the tube in constant motion. Result?

When the tube is full of gas, attach a stopper and a delivery tube with its longer arm turned down. Fill a dry test tube with the evolved gas by displacement of air.

b. Invert the test tube of gas in a beaker of water, and leave it a few minutes. Result? Test the residual gas with a pine splinter having a spark on the end of it. Result?

c. The brown gas is nitrogen dioxide, NO2, mixed with nitrogen tetroxide, N2O4.

The equation is,

Pb(NO3)2→→→→PbO+N2O4(i. e., 2 NO2)+0.

d. The lead oxide in the test tube may nearly all be

removed by adding to the cold tube dilute nitric acid and heating carefully.

EXPERIMENT XXXVII.

NITRIC OXIDE.

Apparatus. Generating bottle (250 c.c.), two stoppers (one two-holed and one one-holed), funnel tube, delivery tubes, pneumatic trough, wide-mouth collecting bottles, cardboard or glass covers.

Materials. Copper (granulated or turnings), nitric acid, ferrous sulphate, splinter of pine, red phosphorus.

a. Into a generating bottle (250 c.c.) put enough granulated copper to cover the bottom. Attach stopper containing funnel tube and delivery tube. Add through the funnel tube enough dilute nitric acid to immerse the lower end of the tube, and then concentrated acid, as necessary, to give brisk action. The gas produced is nitric oxide, NO. If the acid is too concentrated, considerable nitrogen tetroxide is produced.

gas,

and expose

b. Fill a bottle over water with the it to the air. Result? From the result tell why the gas in the generating flask was originally brown.

c. Pass the gas about three minutes into 10 c.c. concentrated ferrous sulphate solution in a test tube.

Save the solution for g.

Result?

d. Collect a second and a third bottle full of the gas over water. Cover one of the bottles, remove it from the water, turn it mouth upward, and put into it a lighted splinter. Result?

e. Repeat d with the last bottle of the gas, using a deflagrating spoon containing briskly burning red phosphorus, instead of the splinter. Compare results. Is nitric oxide a supporter of combustion, or not?

f. Attach to the test tube of solution from c a oneholed stopper and a delivery tube. Warm gently and collect the evolved gas over water in a test tube. Expose the gas to the air. Result? Conclusion?

The brown liquid obtained in c contains a compound of ferrous sulphate and nitric oxide (FeSO4.NO).

See Experiment XXXIV, f, where the formation of a brown ring of this compound was used as a test for nitric acid and the nitrates.

g. Pour 25 c.c. of the solution (its color?) left in the generating flask into a beaker, add any unused copper, and let the beaker stand (in a gas chamber if possible) until all action ceases. There should be an excess of copper. Pour the liquid into an evaporating dish, and evaporate on a wire gauze to about 10 c.c. Dip into the liquid a glass rod, and see if the liquid which sticks to the rod will solidify on cooling. If so, let the dish cool; if not, evaporate off about 2 c.c. more, and try again. Result?

The substance obtained is cupric nitrate, Cu(NO3)2. Write the partial and complete equations.