4. The Effect Of Different Degrees Or Thicknesses Of Insulation

Materials

The same as those used in the experiment, section 1, with the addition of boxes of various sizes, some smaller, some larger, than the one used in the first experiment.

Pack the boxes with one or more of the various insulating materials used in the first experiment, so as to allow varying thicknesses of insulation around the cooker-pail. This should be the same or an exactly similar pail in each case. Fill the pail for all tests with an equal quantity of water, boil it for one minute, and leave it in the boxes for an equal length of time. Record the temperature maintained in each test. Keep the record in tabular form.

What thickness of insulation do you find gives the best result with the materials used in your experiment? Is it necessary to assume that the same thickness will be required with all insulating materials?

5. The Effect Of The Density Of Foods Upon The Temperature Maintained

Materials

One cooker or hay-box

Starch

Water

Salt

Cooking thermometer

Scales

Litre or quart measure

Notebook and pencil

Bring one or more litres or quarts of water to a boil, boil it for one minute, and put it into the cooker for one hour or more. Repeat the test, using, successively, five grams of salt to each litre, or one teaspoonful to each quart, and 5, 10, and 20 per cent. mixtures of starch with water. Record the temperatures in tabular form, and compare the results. What would you gather to be the effect of density upon the temperatures maintained?

6. The Effect On Temperature Of Filling The Cooker-Pails One-Fourth, One-Half, Three-Quarters, And Entirely Full

Materials

Cooker or hay-box pail of eight quarts' capacity Pail of two quarts' capacity

"Space adjuster"

Water

Thermometer

Notebook and pencil

Fill the large cooker-pail one-fourth full of water. Bring it to a boil and put it into the cooker for a definite period of time, not less than one hour. Record the resulting temperature. If desired to make the test more comprehensive, leave the water in the cooker for six, nine, or twelve hours, being careful to allow the cooker to become cold between each test. Perform the same experiment with the same pail one-half full, again when it is three-fourths full, and again when entirely full. Record the results in tabular form and compare them. Repeat these tests with a pail of two quarts' capacity. What is the influence on temperature of having pails partially, or completely, filled?

The explanation is that evaporation takes place in partially filled pails.

7. Chemistry Of The Action Of Food Materials

7. Chemistry Of The Action Of Food Materials {salt, soda, acids, water, etc.) upon cooking utensils made of tin, or aluminum, when used in a cooker or hay-box.

The amount of tin dissolved by foods is indicated by the corrosion of the utensil, which can often be seen by the naked eye to be altered in appearance. The exact quantity of tin salts or other tin compounds which may be formed can only be determined by careful chemical analysis. It has been found that many canned goods supposed to be inert, such as squash and pumpkin, have a marked effect upon tin. Crude tests with a number of different foods can be made with tin, iron, aluminum, and copper utensils, as in many cases there is evidence to the eye of action upon the metals. It must be borne in mind, however, that such tests are crude and not decisive of the fact of there being no action in case no action is plainly visible. Only chemical analysis can prove this.

The action of foods upon tin cans bears a close relation to their action upon the utensils when used in fireless cookery, since there is time with the long cooking involved for similar reactions to take place in the cooker.*

Tin utensils rust badly after short use in a cooker, and thus affect the flavour of food cooked in them. This is due to the action of acids and water on the iron which forms the basis of sheet tin. When the thin plating of tin is worn off, the iron is left exposed to the action of water, etc. Soda dissolves aluminum, and leaves a black surface on aluminum utensils. This black substance is iron, which is present with the aluminum in the utensils. To remove the black appearance, clean the utensil with acid. Do not try to remove it by scouring, as this will not do the work well, and is laborious and injurious to the pail.

* See "Food Inspection and Analysis," by Leach, published by John Wiley Sons, New York, 1904, page 694.

Detection Of Poisonous Metals That May Be Dissolved From The Cooker Utensils

Experiment A. Tin

In a tin cooker-pail boil such foods as apple sauce, tomatoes, squash, or others that act on tin, and put them into a cooker for twelve hours. Transfer them to an agate ware or porcelain utensil, evaporate them over steam until they may be burned in a porcelain dish until charred and brittle. Pulverize this charred mass, and extract it with hydrochloric acid. Filter and wash it. Saturate the fitrate with hydrogen sulphide gas; add a saturated solution of potassium acetate to neutralize the hydrochloric acid present and assist in the coagulation of sulphide of tin. Warm it slightly, filter and wash out the stannic sulphide, dry it and weight it as stannic oxide, from which the tin dissolved may be calculated.

Experiment B. Aluminum

To simplify the experiment a weak solution of malic acid may be used (seven grams per litre being about the average amount found in apples). Bring this to a boil in an aluminum cooker-pail and put it into a cooker for twelve hours. Transfer it to a porcelain vessel and add ammonia to precipitate the alumina. Filter and wash this, dry and weigh the aluminum oxide. It is probable that a smaller quantity of aluminum would be dissolved by foods of a mushy consistency than would be found in this clear solution.