reaction. Some heat has been absorbed by the calorimeter beaker, the thermometer, and the stirrer, and this must be determined and added to the apparent heat. If the materials are of the character specified, experiment has shown that the heat absorbed will be about 12 cal., and this value may be assumed with little error. The constant may be calculated by determining the weight of the portion of the beaker and stirrer in contact with the water, multiplying this by 0.19 (the specific heat of glass), and to this adding the volume of the submerged part of the thermometer, multiplied by 0.49.

Having in this way found the heat of neutralization of 150 cc. of normal NaOH, calculate the heat of neutralization of 1 gram-molecular weight of the base (1000 cc.). The value determined by accurate experiment is 13,700 cal.

140. Heat of solution. Accurately measure 300 cc. of pure water into the calorimeter beaker A (Fig. 47). Grind about 15 g. of potassium nitrate to a very fine powder in a mortar, and place it in a test tube. Weigh the tube and nitrate very accurately and immerse the lower end of the tube in the water in the calorimeter until the nitrate has come to the temperature of the water (about fifteen minutes). Make a note of the temperature. Remove the tube with as little loss of water as possible, roughly dry it with a towel, and at once pour most of the nitrate into the water. Quickly replace the covers, as in § 139, stir vigorously, and note the lowest temperature recorded. Then weigh the tube and the remaining nitrate, deducting this weight from the original one to get the weight of the nitrate added. From the data so secured, together with the calorimeter constant, calculate the heat of solution of 1 gram-molecular weight of potassium nitrate. Berthelot found this to be - 8300 cal.

CHAPTER XVII

BORON AND SILICON

141. Borax bead. a. Make a little loop on the end of a platinum wire and heat it to redness in a Bunsen flame; then quickly bring the loop in contact with some borax and reheat. The borax adhering to the loop will swell up (why?) and finally form a clear glass bead. Now dip the bead into a solution of a cobalt compound and reheat (R).

b. Repeat the experiment, substituting a compound of chromium for the cobalt solution.

142. Boric acid. a. Dissolve 5 g. of borax in 15 cc. of boiling water. Test the solution with litmus paper. Explain. Add to the hot solution 5 cc. of concentrated hydrochloric acid. Cool the solution, filter off the precipitate (R). Compare the precipitate with borax as to solubility in alcohol.

b. Place 1 cc. of a solution of borax in an evaporating-dish and add a few drops of sulfuric acid (R) and 2 or 3 cc. of alcohol. Set fire to the alcohol and watch for a green color in the flame. This is a test for boric acid. Will borax act in the

same way if no sulfuric acid is added?

c. Heat a little boric acid in an iron crucible until a clear liquid is formed (R).

143. Borax. Prepare a concentrated solution of borax and add a few drops of a solution of silver nitrate. The precipitate is silver borate (R). Add a few drops of the concentrated solution of borax to a test tube half full of water, and then test with silver nitrate. The precipitate is silver oxide (R). Compare it with the precipitate formed by the action of very dilute sodium hydroxide on silver nitrate (R). How do you account for the different actions of borax on silver nitrate ?