18 THE ANALYST. CORRESPONDENCE. [Th Editor is not in any way reqionsible for q&-hiw eapressed by his correspondents.] To tlle Editor of the ANALYST. SIR,--I find in the last number of the ANALYST, in the report of the discussion on my paper, some remarks by Dr. Alder Wright on the plummet-method of taking specific gravities. I answered his criticisms on the occasion of the meeting, and uilderstood that such parts of the discussion as would appear in the ANALYST were all replied to in the nbst’raot of my remarks published on page 230. This, however, is not the case, as no reply appears to Dr. Wright’s criticisms. I shall therefore be obliged if you will allow me space for the following comments. In the first place there is a dist-inct practical advanta.ge in comparing with water at the ordinary temperature taken as unity the figures obtained with oils a t the boiling-point of water.This is in con- sequence of the construction of the Westpbsl Balance, and similar pieces of apparatus, and the weights used therewith. Practically, the numbers I give as expressing the densities of oils are the relative weights necessary to be used to counterpoise a plummet which is counterpoised by 1 gramme when immersed in distilled water at 1 5 O C. If the figures which were the actual result of observation were to be com- pared with water at the boiling-point as a standard, a troublesome calculation would be necessary, and, as Dr. Wright points out, the results would be vitiated to R certain extent by well-known causes. But I would point out that the value of the figures as accurate expressions of the relative weights of equal measures of liquids a t the boiling-point of water, compared wit4 thab of an equal measure of water at the ordinary temperature, is a very different thing from the oolutancy of tl@$pres obtained.Thus, it may not be zt fact that a cubic centimetre of butter-fat at 9gP C. weighs %80 gramme, but it is a fact that a particular sample of butter-fat which gives an indicated density of ‘8680 at 9 9 O C. by the Westphal balance will, on repeating the experiment, give a figure not varying by more than *0002 from that first obtained. Practically, what we desixe to know is the in&ioated cmnparativs density under the conditions in question. In the present condition of chemistry there is absolutely no useful deduction to be drawn from the density of a liquid fat, except in comparison with the density of other fats ; and if the observations be so made as to render all the results comparative, every object having either a theoretical or practical interest is attained.If any one have any desire for a more complicated mode of expression by all means let him adopt it, but I feel sure that analysts generally will prefer to employ figures obtained by directly reading off the indications of the balance, than certain other figures derived from the last by a somewhat complicated series of considerations, and which, in case of necessity, it would be perfectly impossible to get the average magisterial or lcgal mind to follow. I fully agree with Dr. Wright in his objection to such expressions as ‘‘ specific gravity a t 1OOQ compared with water at 159,” and have indicated my views pretty strongly elsewhere (“ Commercial Organic Analysis,” vol.i., page 7). The difficulty is to find some short mode of expression which would have a chance of being generally adopted by chemists, and which would express what was really meant. As pointea out by Dr. Wright, owing to the expansion o€ the plummet, the actual weight indicated would not be accurately the weight in grammers of 1 cubic centimetre at the boiling-point. In default of a better, I would suggest the term “ i n d i c a t e d p Z ~ ~ t . ~ ~ a ~ ~ ~ t ~ ” for expressing densities indicated by the plummet method, and would add the temperature of the liquid in each case ; it being understood that the plummet is one which indicates mnity when immersed in water at 15O C.Thus the ‘‘ indicated plummet-gravity ” of butter-fat at 999 C. ranges from -8670 to WOO, with an average of .8680 ; while butterine usually indicates between *8585 and -8625 under similar conditions. -1 am, sir, yours truly, ALFRED H. ALLEN. 1, Surrey Street, Sheffield, December 21st, 1886. “ADDING SALT TO MILK.” To thc! Bditor of the ANALPBT. DEAR SIR,-With reference to the footnote on the above case, this is not the first conviction in Scothnd for a similar offence. I enclose a newspaper report of the case which was tried on March 12th, 1876. Kindly return the inclosure, and make the correction in your next issue.-Yours truly, 86, Raglan Road, Smethwick, near Birmingham, 16th December, 1886. W.MCCOWAN. BOOKS, &c., RECEIVED. AMERICAN Analyst ; American Chemical Review ; American Druggist ; American Grocer ; American Journal of Pharmacy ; Brewer’s Guardian ; British and Colonial Druggist; Canadian Pharmaceutical Journal ; Chemist and Druggist ; Country Brewer’s Gazette ; Hospital Gazette ; Illustrated Science Monthly; Independent Journal ; Invention ; Journal of the American Chemical Society ; Journal of Microscopy and Natural Science; Justus Liebig’s Annalin der Chemie; Journal of the Society of Chemical Industry; Le Mouvement Hygienique; Manual for the use of the Board of Health of Massachusetts ; M e d i d Press ; Hedical Record ; The Miller ; Monthly Magazine of Pharmacy and Chemistry ; National Druggist ; Outlines of Quantitative Analysis, by A. 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