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ANALYTICAL EDITIOIV
ence. Iron, molybdenum, uranium, and vanadium must be absent.
Literature Cited
(3) Hillebrand and Lundell, “ilpplied Inorganic knalysis”, p. 370, Ken. York, John R’iley & Sons, 1929. (4) Walden, Hammett, and Chapman, J. Am. Chem. Soc., 55, 2649 I , no“\
(1) Birnbaum and Walden, J . Am. Chem. Soc., 60, 64 (1938)
(2)
15;
Fryling and Tooley, Ibid.,58, 826 (1936).
\rYso).
Walden, Hammett, and Edmonds, Ibid.,56, 350 (1934). (6) Willard and Young, Ibid., 55, 3260 (1933). (5)
Still for Producing Metal-Free Distilled Water J. S. 3ICHARGUE ‘ N D E. R. OFFUTT h;rntiirky Ipricwltural Experiment Station, Lexington,
A
?;I -4DEQUATE supply of distilled water, which is free
from metallic and nonmetallic compounds, is of fundamental importance for research investigations planned to show the necessity of the minor elements in the economy of plants and animals. I n this article the term “metal-free dietilled water” is used to designate water containing total metals of the order of one part per billion or leis
A
B
C
FIGURE1. FORNS OF QUARTZ CONDESSER TUBES
It is well known among chemists that distilled water that is produced with the ordinary type of water still contains small amounts of a number of metallic elements, including copper, zinc, tin, lead, manganese, nickel, and iron. These elements can be detected when several liters of the distillate are evaporated to dryness and sensitive tests are carefully applied for the respective elements. It has been shown in previous work that distilled water made with the type of still commonly used in chemical laboratories contains a sufficient amount of copper and zinc to supply the requirements of plants for these elements, when it is used as the source of water in water or sand cultures. hIetallic elements arc introduced into distilled mater from the processes of oxidation, erosion, and solution of the
Ky.
condenser tube, which is usually constructed from brass t u b ing and coated on the condensing surface with tin. The principal ore from which tin is smelted is cassiterite, or tin oxide @nos), n-hich in the crude state contains arsenic, bismuth. zinc, copper, manganese, and iron. The usuai process for the purification of tin seldom frees it from traces of these metali Condenser tubes made from metals are used because the\ are cheap and conduct heat more efficiently than tubes maclc~ from earthenware materials such as porcelain ot silica. Purc platinum is undoiibtedly the most desirable metal for makirig condenser tubes. h i t the cost is prohibitive. It is a1.o like]\ that traces of this metal could be detected in a few liter,. 01 distilled water made n i t h a platinum condenxi. In recent yeat + quartz vessels of small size for making snixll quantities 01 conducti\ity water hare been sold by dealer. I I I cheniical appaiatu+ For several yc’arb the senior author ha% endeavored to produce distilled ~ ’ ater r free of metals by usiiig condensers made of quartz, as shown in A and R, Figure 1. A represents a straight, thin-walled quartz tube which wplaced the metal condenser tube, in a gas-heated n a t e r htill of the Stokes type. B shons a condenser tube made froin quaitz by the Thermal Syndicate oi S e w Tork according t o the authors’ design K h e n proper11 housed and installed tin. type of condenser will produce about 5.7 liters (1.5 gallon.) uf metal-free distilled water per houi . K i t h the recent inqtallation of a central heating plant I t this university >team became available for usi’ in the 1aboi:itories. X larger size quartz condenser of the fcrm shonn by (’ in Figure 1 nas designed by members of this department anti n-ab cuonstructed according to their plans by thl: Amersil Company of S e w ’Jiork. The boiler and housing for the condenw were constructed in the shops of the Departnifnt of Buildings and Grounds of this university. Figure 2 is a detailed drawing of the still. A and E are thP brass end plates of the condenser jacket which were cast and machined to the desired form and dimensions; B and F are packing joints a t the ends of the cordenser tube; C and I are 907-gram (32-ounce) sheet copper tinned on the inside, from which the boiler and the condenser jacket vere made; D and H arc brass rings attached t o the walls of the condenser jacket and boiler, respectively. Grooves were machined into the upper surfaces of these rings in which is placed rope packing to make tight joints when plate E and boiler lid G are bolted in place. J is a steam coil; K and L make up a device for maintaining a constant water level in the boiler; Af is the overflow from the condenser jacket; N is the steam pipe t o the condenser; and 0 iy the clamp for holding the porcelain cap in place. The heavy arrows indic:rt,p the path of steam from the boiler t o the condenser tube. The cock on the tube connected to the bottom of the boiler allows the slush and scale Ivhich accumulate in the boiler to be washed out when necessary and permits the boiler t o be kept comparatively clean from residue. Figure 3 shows the still mounted and ready fcir use. It has a capacity of about 11 liters (3 gallons) of metal-free distillate per hour a t the temperature of the tap lmter, but’ when the distillate
INDUSTRIAL ANI) ENGINEERING CHEiMISTRY
158
is allowed to flow from the condenser a t a temperature of about 80" to 90' C. the capacity is approximately 13 to 15 liters (3.5 to 4.0 gallons) Der hour. The distillate flows from the auartz condenser through a glass adapter made of Pyrex glass inio the acidresistant, IOO-liter, stoneware reservoirs. These are connected by a siphon made of Pyrex glass tubing Thich maintains the same water level in the reservoirs. A level gage, made of small-size Pyrex tubing and placed between the reservoirs with a graduated
VOL. 12, NO. 3
scale attached, shows the quantity of water in the reservoir at any time. With approximately constant steam pressure and the proper adjusting of the and n,ater valves, the operates satisfactorily with very little attention and has been run continuously overnight, without attention, for several
WATER
STORAGE
I/-J
DIAGRAM OF STILL FIGURE2. DETAILED
MARCH 15,1940
ANALYTICAL EDITIOA
IS9
sample of the mater. Accordiiig to the3e ~nvestigatorsthr. presence of very small quantities 0' one or more of the following metals may be detected with this method: zinc, copper, lead, nickel, cobalt, mercury, cac'mium, thallium, and bismuth. I n the authors' case, the impurities n; inld probably be copper, lead, and zinc. It has been found, in this laboratory, t metals listed above do not display equal a11 the test color with dithizone, the method of' testing is very sensitive. Using care, it is posdile to detect as little as 0.1 microgram of zinc, rvhich agrees i x t h the clainis of Stout and Arnon. Using a standard solutio11 of zinc. and comparing thr color developed by clithizoiie with 1;he standard and wiDh that produced with the concentrate from 2 liters c;f distilled water. using a microcolorimeter, it was found that the distilled water contained 0.2 part per billion of total metals (as listed above). The conductance of a sample of the distilled r a t e r was measured, taking no special precaution to esulude carbon dioxide or fumes generally present in a chemical laboratory. The specific conchctance, as measured, TT':LS 2.88 X reciprocal ohm. From the above tests, tlie authors are of the opinion that the distilled water produced by t'hk still can br regarded as free from metallic' compounds as it is posi:ible to produce mater in the quantity shown with Y single distillation. I n investigations prrtaininp to ilie study of the effects of the minor elements on gron?h s.nd development, of both plants and animals, large volumes of clistilleti Jvater are consumed daily. Because distillation of miter f , m m an ordinary still would be both t,irne-consuming and trou.blesome, such a strill as has been dw(:rihed a1m-e j c of great, importance.
Literature Cited (1) Stout, P. R.,and . I m o n , D. I., Am,. .T. Rotan!/, 26,144-9 (1939)
FIGURE 3. STILL INSTALLEI) 1. Drain from sweat pan 2. Valve f o r cleaning o u t condenser jacket 3. Valve regulating flow of water into condenser jacket 4. Drain pipe for boiler 5 . Steam inlet valve 6. Clean-out valve for boiler
days in succession. The reservoirs were placed in a leadlined basin, which was connected to a drain pipe in caw of overflow.
A Ten-Liter Volumetric Flask FRANCIS ,J. REJTHEL
Tests for Purity of Distillate
University of Oregon 3Iedical School, Portland. Ore.
After the still had been in operation for several months a sample of distilled water was collected in a thoroughly cleaned Pyres flask. A 3.5-liter portion of the sample was evaporated to a small volume in a new Pyrex glass flask, which was attached to a condenser with a ground-glass connection. The concentrate was transferred t o a weighed platinum dish and evaporated t o drynew in an oven. The following results were obtained: Total solids (evaporated a t 110' C.), 0.00029 gram Ignited solids (750' C i,0.0001 gram per liter
THE investigation reported here was carried out in connection with a project of the Kentucky Agricultural Experiment Station, Lexington. Ky.. and is piihlished by t h e prrmission of i h e Director
liter
Another test was made on a 10-liter sample of water, using the above-described technique, with the following results: Total solids (evaporated a t 110' C.), 0.00037 gram per liter Ignited solids (750' C.), 0.00015 gram per liter
The reaults of this last test are equivalent to 150 p. p. b. of ignited total solids. Most of this residue was silica which had been dissolved from the condenser tube and Pyrex flask used in concentrating. A negative test for iron in the water was obtained, using the sulfocyanate method, indicating that iron, if preqent a t all, &-asless than 0.5 part per billion, which is the limit of sensitivity of the test. The dithizone test for "total metals'' described b y Stout and .irnon ( 1 ) was made on the cnnwntrate from a 2-liter
HEX making large quantiti1.s of staniiard solutions a large volumetric flask is desirable. In the author's laboratory this is provided by fitting a 12-111rr Pyrex bottle with a simple volume indicator. A graduated pipet is inserted through a rubber stopper that is large enough to rest flat on the neck of the bottle. Exactly 10 liters of mater (or any other desired volume) a t room temperature are put into the bottle, arid the pipet is adjusted so that the tip barely touches the surface of tlie liquid. If a 10-ml. pipet is used, the graduations near the top will be partly covered b y the stoppel, b) that whcn thP pipet just touches the surface of the liquid the, lon-er surface of tlie stopper will correspond to some reading on the pipet-say, 2.2 ml. The pipet can be readjusted in;tantaneously by resetting the loner surface of the stopper to the propel mark. Any volume in the flask will corre-pond to a mark on the pipet, the readings becoming greater witli larger volumes as the pipet is pushed up through tlie stopper, and a eimplr table may be prepared shoving r d i n g s for \ arious volumes The pipet itself is never immersed in the liquid. \Then the apparatus is carefully adjiistetl, t h c volume can he measured tn * 5 ml.
