Jan., 1912
T H E J O C - R S A L OF I.VD C - S T R I A L A N D E S G I S E E R I S G C H E M I S T R Y .
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LABORATORY AND PLANT. AN ELECTRIC LABORATORY FURNACE. B y RAYMOXD C.
GESNER.
Received August 16. 1911.
I n taking up the subject of methods of ignition, we must, of necessity, go back to the time of Bunsen. He would feel quite a t home in this field, for, here, things have been a t a standstill and we have remained about where he left us until within the last year or so, since which time more attention has been given to this important subject. I n most places t.he Bunsen burner and air blast furnish the sole sources of heat for ignition purposes. In order t h a t a given compound may have a definite and constant composition for weighing, both the manner and temperature of ignition must be taken into consideration. I n the case of many elements such as silicon and calcium, the form in which they are usually weighed is not altered by the highest temperatures obtainable with the Bunsen burner or the laboratory blast lamp. For such as these, this method of ignition may be used with perfect satisfaction. Another factor, however, t o be reckoned with, is the loss of weight undergone by the platinum crucibles when ignited in the open flame. By heating a platinum crucible weighing about r j grams bj- means of gas, which contained considerable sulphur, the author has found this loss to be as high as I mg. per hour. The question of temperature is likely to be the one of most importance, and one in which the analyst is most likely to err, since the various texts give but an idefinite idea as to the maximum temperature which certain precipitates mill stand before undergoing decomposition, or, on the other hand, as to what temperature it is necessary to use in order to obtain a compound of definite composition. Treadwell’s“Analytical Chemistry,” N.Y . ,1910, p. 167, says, in regard t o the ignition of cadmium sulphate in a double crucible: “The outer crucible can be heated to the full red heat of the Teclu burner without running risk of decomposing the cadmium sulphate. I t is, however, not necessary to heat i t so strongly.” In regard to the ignition of manganese sulphate, the following statement is found in Fresenius, ‘cQziantitatizv .-lnalysis”, N . Y., 1896, p. 158: “ I t resists a very faint red heat, but upon exposure t o a more or less intense red heat, it suffers decomposition.” Electricity makes the most convenient, cleanest way of obtaining heat for many laboratory purposes, but when platinum resistance furnaces are utilized, the likelihood of their burning out, as well as first cost, often makes their use prohibitive. With the advance in the study of alloys, i t has been found that an alloy of nickel and chromium, called “Nichrome.” possesses properties which make it a n ideal wire for laboratory resistance furnaces for temperatures up to a maximum of I I 0 0 O C. This alloy which melts a t about 2800’ F. is not easily corroded b y ordinary laboratory fumes and has a resistance of about 68 times that of copper. This high resistance makes it possible to use
electricity a t I I O to 2 2 0 volts with very little, if any, external resistance in the circuit. This renders possible the construction of small laboratory furnaces for temperatures up to I O O O O C. or 1100’ C . , not only a t low cost, but with the additional advantage of economical operation because of the utilization of the currents ordinarily a t hand. The furnaces most largely
I
Fig.
1.
employed by us are of two types, but being made in the same general way, a detailed description of one will suffice. Somewhat similar combustion and treating furnaces have been described by Berry.1 The furnace shown in Fig. I has for a foundation a small clay cup, such as is used in batteries. I n the case of this furnace, i t is z l / ” ’ in diameter and j” long, which size
* THIS JOWRNAL,
2, No. 6.
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T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y .
is very convenient for individual use. When resting on end i t has been used for making fusions and when resting on the side, for ignitions. This furnace can be made t o hold four crucibles a t a time b y inserting a long piece of asbestos board to form a bottom. Around the clay cup A is wound the “Nichrome” wire, the size and length of which may be easily determined, when the size of the clay cup and the voltage of the current to be used are known. One half the carrying capacity of the air-cooled wire, as allowed by the manufacturers in their bulletin (this can be obtained on request), should not be exceeded when the wire is enclosed in heat-insulating material, as we describe. In order that the furnace may not be readily burned out, wire of such size and length should be used for each furnace that i t will be impossible t o exceed one-half the carrying capacity of the wire when there is no resistance in the circuit. I t must be remembered that a temperature of 1000’ C. within the furnace means that the temperature of the wire carrying the current is much higher. After determining the length of wire with which the furnace is to be wound,
Jan.,
1912
will insulate, a t the same time have no chemical action on the wires and yet protect them from the air a t 1000’ C., is more or less of a problem. Of the mixtures which have already been tested, the one consisting of one part kaolin t o three parts of ground quartz gives the best results. The kaolin and crushed quartz are mixed to a paste with water and plastered over the wire and cup, care being taken t o fill all 5
A
d
ip
‘\ \
472 the winding may be commenced a t the closed end of the muffle A (Fig. I ) , enough free end being left to reach the binding post E. The wire is fastened b y several turns of nickel or “Nichrome” wire of a larger size than that used in winding the furnace. The wire on the outer end of the furnace is wound a little close in order that the temperature may be equalized where radiation is greater. Great care should be used to avoid kinking the wire, as this renders it brittle. When the winding is complete, the end is fastened in the same manner as before, leaving enough free end t o reach the binding post E’. After the winding has been properly executed, the problem of proper insulation and protection from the air is t o be considered. The insulation in itself is not difficult, but to find a material which
Fi9. 3 space between the wires B (Fig. I ) . This mixture is plastered on just thick enough to completely cover the wires. (If the coating is too thick i t is likely to crack badly.) After drying and baking by means of the current, any imperfections are repaired and the baking repeated. This can be somewhat improved by painting with a dilute solution of water glass. ATow the furnace is ready for packing in the heat
Jan.,
1912
T H E JOCR-YAL OF I - V D C S T R I A L AA-D E S G I i Y E E R I - Y G C H E M I S T R Y .
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insulating material D. This is done as shown The slide contact is made of hard wood, the hole in in Fig. I. The whole is then covered with a heavy the center being lined with copper b y means of which piece of asbestos board F, and the binding posts E contact is secured with the sheet of brass or “Nichrome” ribbon. The metal is kept in contact with rod are placed a s shown. A furnace of the muffle type (Fig. 2) has likewise . 6, which passes through the metal lined hole, by been constructed on the same general principles and means of a small screw. The brass or “Wichrome” has been found t o be equally economical, as well sheet has enough spring t o make a satisfactory as much more satisfactory when a large number of contact, when pressed against the wire, where it winds ignitions are to be made. This furnace is I O I / ~ ” about j by rotating around 6. This arrangement long over all, while the muffle is j * / 2” in length. The is quite satisfactory for currents up t o 3 amperes, furnace is wired with No. 1 7 B. S. “Nichrome” wire. but for higher currents better contact is necessary The same temperatures can be obtained in this furnace and can be obtained by a thumb screw so arranged as in the one first described, but more care must be as to pass through C and press X against the resistance wire (Fig. 6). taken because of its increased size. When cleanliness and convenience are considered, Without external resistance the highest temperature, t o which i t is safe t o heat the furnaces, can be.obtained there is no comparison between the electric furnace when the furnace door is closed. Furnaces, constructed and gas as a means of making ignitions. The first cost of the two furnaces as well as the on .the above plan and of the dimensions shown in the figures, as a rule, fulfil these conditions. Never- resistance box can be seen from the following tables:
theless the highest temperature obtainable in each furnace should be determined and not allowed t o exceed 1000’ t o I I O O O C., if the life of the furnace is t o be considered. I n order that a constant temperature less than the maximum may be obtained, i t is necessary to have external resistance. A very convenient resistance box, shown in Fig. 3, can be made b y using six stove bolts of iron, about 12” long, threaded a t both ends, each end being provided with two washers and two nuts. The ends of the resistance box may be made of either asbestos board or wood, wood being the more satisfactory for boxes, which are t o be used for small currents which produce b u t small amounts of heat. For boxes which are t o be wound with heavier wire and used for large currents, which develop sufficient heat to warp boards, asbestos, although not as stiff, is more satisfactory. The five iron rods, I to j (Fig. 3), should be wrapped with thin asbestos paper which has been painted with water glass solution. The water glass cements the paper firmly t o the iron, so t h a t no trouble will be experienced with its peeling off. Bolt 6 is left bare. When the water glass is dry, the bolts should be fastened in position on the boards as indicated by I to 6 in Fig. 3.
I I U F F L E 1:URNACI.
Xuffle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . \Tire 65 ft. No. 17 B. S. “Nichrome” . . . . . . . . . . . . . . . . . . . Labor a t 50 cents an hour. ............................. Clay and quartz s a n d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Heat-insulating material (old pipe covering).
.............
0.50 1.27 1 .OO 0.10 0 .OO $2.87
CRUCIBLEFURNACE. Clay cup Wire S o Labor a t Clay and
................................. 0.20 . . . . . . . . . . . . . . . . . . . 0.35 0.75 ................................ 0 05
2’,’2‘‘ X 43/,”. 20 B. S. 32 ft. “Nichrome” 50 cents a n h o u r . . ............................ quartz s a n d . ,
$1.35 RESISTANCE Box.
Stovebolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wire 75 f t . No. 22 B. S. “Nichrome” with a resistance of about 70 ohms and a carrying capacity of about 6 amperes.. Labor a t 50 cents a n h o u r . . ............................
........................................
1.00
0.80 2 .OO $3.80
The cost of operation is as reasonable as the first cost. When used on a I Io-volt circuit, with electricity a t I O cents per kw. hour, the muffle furnace, which takes 5 amperes, can be operated a t a cost of 5 cents per hour and the crucible furnace, which takes 3 amperes, will cost 3 cents per hour. At the University
T H E JOCKA\-dL OF I A Y D C S T R I L 4 LA,VD E.YGI.YEERIA-G
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of Arizona. where gas is $1.50 per 1000 cu. f t . , it costs about I . j cents per hour to run a Bunsen burner. Therefore, when, as is the rule, several ignitions are to be made, the electricity is considerably cheaper than gas since 2 t o 4 crucibles can be ignited in the smaller furnace and 4 t o 8 in the large. In these electric furnaces, temperatures can also be reached in a porcelain crucible which are rather difficult t o obtain by means of a Bunsen burner or blast lamp.
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CHEJIISTRY.
J a n . , 1912
and installed by a local tinner at a cost of $21.00, not including the steam trap. I n operation the still is charged with 35 pounds lump lime and 26 liters of ordinary 94 t o 95 per cent. alcohol. A current of water is started through the condenser and steam turned on until the alcohol has been heated t o boiling and then turned off. This takes about five minutes’ time and the dehydration of the alcohol once started evolves sufficient heat to keep the still hot some hours. To insure the completion of the dehydration, the steam is turned on the next morning and the heating with the condenser vertical continued for six or seven hours. The union A is then loosened, the condenser turned down into the nearly horizontal position shown in the sketch,
t
The heating and cooling curves (Figs. 4 and 5 ) , taken with the door closed and open, show the rate a t which the furnace will heat up and cool down. With ordinary usage, furnaces, made as described above, have a life of several hundred working hours and when one burns out i t is only a matter of the expenditure of a few moments of time to renew the heating element. UNIVERSITYO F ARIZONA, TUCSON.
A STILL FOR ABSOLUTE ALCOHOL.: By RALPHH. M C K E E .
Received October 1 7 , 1911.
I n a laboratory, in which considerable organic work is carried on, the expense of absolute alcohol in a year’s time is a distinct item. The still shown in the accompanying sketch has proven efficient in the preparation of absolute alcohol from ordinary 94 per cent. alcohol. I t is made of sheet copper tinned on one side, with a half-inch bent brass pipe (32 inches within the still. A greater length would probably be a n improvement), whose upper end is connected with the main carrying steam a t about 40 pounds pressure and the lower end with the same steam trap used for our still for distilled water. An opening, B, four inches in diameter, is used for filling a n d emptying the still. I t is closed by use of the top of a plumber’s drum trap such as is commonly used in connection with bath tubs. The still was made Another form of alcohol still is described by Warren. J . Am. Chem. Soc..
32, 698
(1910).
the union tightened and the distillation and collection of the absolute alcohol begun. At this point it is necessary to wrap some kind of a blanket about the body of the still, otherwise, owing t o air cooling, the distillation will be slow and incomplete. To clean, the unions are opened and the still removed to a convenient place and washed out b y use of a hose inserted into the four-inch opening B. The yield is somewhat over sixteen liters of alcohol of slightly better grade (99.8 per cent.) than shown by freshly opened bottles of “absolute alcohol” from two well-known German chemical houses. The cost of the product is about $0.30 a kilo as compared with the ordinary purchase price of $1.10 a kilo, both being on the “duty-free” basis granted to educational institutions. Laboratories which cannot avail themselves of “duty-free” straight alcohol may find it worth while to prepare, by this apparatus, water-free alcohol from the ordinary denatured article. JfAINE. ORONO
UNIVERSITY O F
