is rnatlc to contribute to the ”efficiency” of the dryer. My sole contention was t h a t the efficiency of a drying machine was in no way a function of its capacity for heating sand. I dirt indeed point out t h a t the gublished figures required t h a t about 3 3 per cent of the discharged water must be in the form of mist or liquid water, and I said, “if this is possible i t opecs u p a ~ v a pto extraordimry possibilities in drying economies.” This does not appear t o me to difFer from Prof. Lewis’ attitude ol “unlikely but not impossible.” The theory of re-condensation and fog formatioil has been advanced a number of times. I agree absolut.ely with Prof. T,ewis about it, t h a t it is by no means impossible, b u t is unlikely, and t h a t the conditions under which it can occur are unusual. Personally, in a limited experience, I have not come across a n instance where any large supersaturation could be i~ositivelydemonstrated, even under conditions favorable to it. In conclusion as to the dryer question, I hold no special brief for the retention of the word eficiency in connection with the performance of the:e machines although to me personally it is a very useful tool. It is very much easier for me, for instance, to think of a turbiiie as a more e i k i e n t machine than a water wheel, than i t is t o remember their respective outputs of power per unit of energy slipplied T‘ery likely this i.j largely a mental hahit only, h u t the consideration of machines on their eficiency c~xprrssedas a percentage of a n idea! duty is pretty strongly rooted as a custom. Neither am 1 deeply concerned as to whether air drying and Prof. I.ervis leek very strongly about this, so by all means let us trrat them as one. Frankly i t appears to me quite too trivial to develop any strength of feeling about. My suggestion to treat them separately was largely in the interests of convenience xnd expediency, Take only the matter of indexing. Prof. 1,ca.i:’ original letter setting [orth the t,heoretical possibilities o f multiple ekporation contains very much of interest, but thc student ol the subject will seek i t in vain under the heading of “evaporation” and will be indeed fortunate if he searches uiider the caption of “air dryers” for matter relating to vacuum, multiple-effect evaporators. I appreciate Prof. Lewis’ elucidation of the point that I was unable to understand about the evaporation of saline solutions. Of course, iE the vapor temperature is the same as t h a t of the boiling solution the difficulty disappears. As Prof. 1,ewis says, my understanding was t h a t the temperatutre of the \.apor is that of the pure solvent. This i s stated t o be the case h y very many authorities, including Rankine, Box, and many others, and I supposcd was a n accepted and established law. I have happened on only one authority to the contraq-, namely Slendel&eff, who states t h a t the temperature of the vapor is : / ? P .snn?e as t h a t of the solution from which i t is generate?. He proceeds to give the boiling temperatures of sc\-eral solutions of salts and rather curiously adds, “if the temperature of ebullition he determined by immersing the thermometer in the liquid itself,” * * * This qualifying phrase appears to indicate that a correct thermometric indication ca:inot be ohtaiued a t all i n the vapor. o much interested in the divergent statements of authorities on this point t h a t I endeavored t o satisfy myself by a very crude experiment. I took a solution oF caustic soda, boiling approximately a t 120’ C., in a large fiask, starting with the thermomcter bulb immersed in the liquid. TT‘hen very actively hoiling and with the thermometer practically stationary, I raised the bulb just clear of the liquid, when the temperature instantly dropped about 1 2 O, and then remained fairly steady. In this case the thermometer bulb was at a temperature of 1 2 0 ’ and the drop could hardly be due to condensation, and was in thc center of the flask having a surrounding jacket of vapor of about in. on all sides. evaporation zre treatrd separately or as one subject.
I then withdrew the thermometer and wiped the bulb clcarr of caustic soda solution and immediately replaced i t in the vapor,
when the indication was roo’, very slowly rising to about I IO”. The 100’ mark \%;as reached almost instantly, while the subsr quent rise to I I O ” was very slow, requiring many minutes. The same result was obtained by rapidly washing off the thrrmometer with boiling water and plunging into the vapor mhilr still hot, so as t o eliminate as lar as possible condensation on 2 cold bulb. A4gain the temperature of rooo was reached, almost instantly followed by a very slow rise as before. It will be observed: !I) t h a t the clean bulb (free from the solution) in all cases indicated 100’ in the vapor a t first and t h a t t h r subsequent w r y slow rise was coincident with the deposition of the boiling solution on the bulb, from the bombardment from the actively boiling surface; ( 2 ) in 110 case could a reading be obtained anywhere near the boiling point ol the liquid, but a condition of equilibrium occurs about midway between t h r temperature of ebullition and roo’. \Y. 1;. WADMAS B.suoiwz, S s i v J Z R S ~ Y September 10, 1916 I _
ANALYSIS AND MANUFACTURE OF RED LEAD Editor of the Jouuiial OJ” Industrial and Engineering Chenzistry: It may be of value to those interested in the analysis and manufacture of Red Lead to know that a mixture of dilute nitric anti tartaric acids is a n excellent solvent for t h a t substance. T h r hot solution of tartaric and nitric acids dissolves Red Lead almost instantly. The proportion of tartaric to nitric acid i i w r y small. A convenient dilute solvent for Red T,ead is prepared by dissol.i.ing j g. of crystallized tartaric acid in some water, adding to it zoo cc. concentrated nitric acid and the wholr diluted to I liter, Stronger solutions for larger samples are madr by increasing the nitric and tartaric acid contents; thus, i o n C T a solution containing 300 cc. concentrated nitric acid and I 5 g of crystallized tartaric acid per liter will dissolve z o g. of Rpd Lead. Too strong nitric acid must not be kept with tartaric acid as thf latter will decompose on standing. The sol\-ent should be used hot, pouring it over thc samplr and stirring; i t is very much more efficient and also cheaper than hydrogen peroxide which is in general use for Red 1,rad analysis.
GREGORY ’~‘OIiOSSlAA’
CLEVW,WD,OHIO October 6, 1916
DETERMINATION OF SMALL AMOUNTS OF ALCOHOL AND WATER IN ETHER FOR ANAESTHESIA- A CORRECTION I n our article printed under the above title in THISJOURNAL, 8 (1916), 807, an error occurs in Table I. The fraction
Wt. ether $- 1.040533 f 0.9970795 49.84444- I .040550 A- 0.9970770 should read:
+
.040533 X 0.997079,5 ___. x 0.9970770 Also, Heft 7‘111 in footnote 2 , page 807, should read H e f t \-TI.
W t . ether
I
49.8414-t I.040550
ST. Lours September 18, 1916
E. IL’IALLINCKROWr, J R . ,
AND
A . 1). i h T
A STUDY OF T H E EFFECT OF STORAGE ON MIXED PAINTS-C ORRECTION I n the paper by M r Ware and myself as printed in T H I S JOIJRNAL, 8 (1916), 879, the last line, second column, Table I, ” instead of “Na2COd, 3 g.” should read “NazCOa, R. E. CHRIST MA^ ~JKIVERSITP OF MICHIGAN A N N ARBOR,Ostober 19, 1916
