the author succeeded in getting the proper crystals, but he fears their shape may be influenced by temperature, concentration of the liquid, and rate of evaporation, and, therefore, the mere appearance counts for nothing. The following reactions serve to recognise cholerestin: Sulphuric acid gives a reddish-brown, turning to dirty green on adding a drop of water. A mixture of equal parts of chloroform and sulphuric acid gives a violet colour, changing to red and immediately discharged by a drop of water. L. DE K. ON THE ANALYSIS OF OLIVE OIL. RIOUL BRULLE (Rev. Internal. des Falsification, Oct. 15, 1889).-For the testing of olive oil, the author employs argentic nitrate in the presence of fuming nitric acid. The argentic nitrate decomposes violently, and produces metallic silver, with a coloration depending exactly on the nature of the oil employed. If we mix 10 c.c. of an oil with 0.5 c.c. of fuming nitric acid in a porcelain capsule, heat, and shake the mixture violently until a foam has been produced, we obtain different colours, according to the oils employed. We, however, take no notice of these, but go on with the process by adding 5 c.c. of a 25 per cent. solution of argentic nitrate in alcohol of 90°. Still applying heat,a moment arrives, at about 115° C, when the argentic nitrate decomposes, and deposits metallic silver. Having reached this point and continued to heat until the first flecks have just disappeared, we observe, on the one hand, the coloration of the slight oily stratum, which is easily seen by slightly inclining the capsule; and on the other hand, the metallic flecks glistening on the surface of the liquid. On saponifying the oils, and treating them by the same method, the colorations obtained are all different, as may be seen by the following table : After becoming cold, it forms a crystallization of blue-coloured needles on the surface. The designations of the colours are those used in water-colour painting. In comparing the tint of any mixture of oils treated by this method with those given in the above table, a chemist will, after a little experience, be readily able to prove the presence of a seed oil in olive oil, as well as to detect adulterations as low as 5 per cent., and to name the foreign oil present in the sample. M. S. A. M. Gold yellow Gold ochre Bright violet Deep chrome Green [blue THE QUANTITATIVE ESTIMATION OF GALACTOSE. BY E. STEIGER (Zeits. f. Anal. Chem. 28, 444). The author has prepared a table to calculate the quantity of galactose from the quantity of copper reduced; 60 c.c. of Fehling's solution diluted with an equal bulk of water is brought to boiling; 25 c.c. of the galactose solution, previously warmed, is added, and the mixture heated 3-4 minutes. The filtration was done by Soxhlet's Asbestos Filter (see Fresenius' "Quantitative Analysis," 6th edition, p. 596), and the copper oxide reduced in a current of hydrogen. The time-3-4 minutes-must be adhered to, Allibon (Journ. f. Prakt. Chem. 22, 72) having shown that by long heating (half an hour) a further precipitation of cuprous oxide occurs. The author's experiments show that from 3 to 7 minutes' heating, the results are the same. The following table gives the mean of his results, obtained from two different samples of galactose, four estimations being usually made for each dilution : COLOURED ANALYTICAL TABLES SHOWING THE BEHAVIOUR OF THE MORE COMMON METALS AND ACIDS TO THE ORDINARY REAGENTS, WITH SPECIAL REFERENCE TO THE COLOUR of THE VARIOUS OXIDES, SALTS, PRECIPITATES, FLAMES, BORAX-BEADS, AND BLOWPIPE REACTIONS. A CLASS-BOOK FOR STUDENTS IN HOSPITALS, COLLEGES, AND SCHOOLS. BY H. WILSON HAKE, PH.D., F.I.C., F.C.S. London: G. Philip & Son, Fleet Street. THIS book, with so voluminous a title, and a preface nearly filling two pages, is simply a set of the usual sort of imperfect analytical tables served up to the budding aspirants for ordinary medical primary examinations, and sufficiently full to get them through their arduous analytical labours in the (so-called) class of practical chemistry. It, however, differs from all other books with which we have met (except Dr. Simon's "Manual of Chemistry," published in 1885 and reviewed at the time in our columns), inasmuch as that, attached to each test there is a picture of a test tube showing a hand-painted representation of what the colour of the precipitate should be (supposing, of course, that the student works properly); and there are also similarly coloured representations of blowpipe beads, and charcoals, and of bunsen flames. What real advantage there will 66 be to the student other than enabling him to skulk his practical chemistry class even more than he now too often does, and grind up at home, it is difficult to see. But that it will be useful to the unfortunate demonstrator who is expected to teach practical chemistry to perhaps thirty men all at once, is quite evident. This is the real use of such illustrated books; and Dr. Hake lets the cat out of the bag in his preface, when he says: The book, I believe, should prove of service in schools, or in large classes where individual attention from the teacher becomes difficult, or almost impracticable; and medical students who, under the present regulations, have a good deal of simple analysis to learn in a comparatively short space of time, will possibly find their labours lightened by its use." There is no doubt that all those hospital and school teachers who like to take the least possible trouble over their work will find it well worth their while to quietly introduce Dr. Hake's illustrated tables to the notice of the class. Like many such books, it is here and there a little slipshod, as witness the paragraph on metals, in which a student, having been told that he must not use HCl, but nitric acid, to dissolve Pb, Hg, and Cu, is yet left in doubt as to whether he might not use hydrochloric acid for Ag. Surely it would have been just as easy to put the Ag in the nitric acid set and be done with it. So far as the colouring goes, it is really very well done indeed, and quite amusingly natural in many cases, and as we said before, the book is a real boon to the overworked or lazy teacher, and to the "wagging" student. LAW NOTES. CONDENSED SKIM MILK.-An oilman named White, carrying on business in Camberwell-road, was summoned at Lambeth Police Court, for selling condensed milk not of the substance and quality represented, according to the terms of the Adulteration Act.-Mr. Biron, barrister, instructed by Mr. Marsden, vestry clerk of Camberwell, appeared to prosecute; the defendant was represented by Mr. Besley.-George Dewey, one of the inspectors of the Camberwell Vestry, stated that he went to the defendant's shop and asked for three tins of condensed milk. White asked him what brand he would have, and he replied the "Standard" brand. There were several other brands there. He paid 9d. for the three tins. Witness now produced the certificate of Dr. Bernays, the analyst for Camberwell, which showed that 90 per cent. of the cream had been abstracted. -Dr. Bernays in his evidence stated that the certificate produced was given by him. The label upon the tins sold was as follows: "The Standard Brand is specially prepared from the richest cow's milk from which a portion of the cream has been removed, and nothing added but cane-sugar. It is better and cheaper than fresh milk for ordinary purposes. Five parts of water to one of milk, and for infants 8 to 15 parts water, according to age." There had been nothing added to the milk but cane-sugar.-By Mr. Biron: Such a preparation so diluted would not be fit food for infants.-Mr. Besley said the "Standard" brand was a good milk, and then proceeded to quote several decisions with regard to such cases, and contended that the defendant was not liable.-The defendant was called and stated that he sold the milk in question and other brands at 3d., 4d., 44d., and 54d. He declared that he told the inspector it was partly skimmed, and was sure he called the attention of the officer to the labels on the tins, which showed it wa skimmed milk.-Some legal arguments followed, and Mr. Biron (the magistrate) said it no dout was an important and difficult case. Under all the circumstances, however, he felt bound to con vict, although at the same time he was fully satisfied the defendant was without the slightest blame or had any intention to defraud. He should, therefore, only be too willing to grant a case for the various points to be argued in a superior Court. He considered the sale was one to the prejudice of the purchaser under the Act, and he therefore ordered defendant to pay a fine of 20s. and costs.— Notice of appeal was given. CORRESPONDENCE. [The Editor is not in any way responsible for opinions expressed by his correspondents.] To the Editor of the ANALYST. SIR,-In your current issue you are correct in ascribing to me the first mention in your columns of the phenolsulphonic test for nitrates and the napthylamine test for nitrites in water (Vol. x., p. 199; Vol. xii., pp. 50, 152). It will be seen by reference to my papers that the extract from Dr. Leffmann's book approaches very nearly to a copy of my words. The same weights are given for preparing the reagents, and the same precautions directed to be observed. The only practical differences I have noticed are, the introduction of a glass rod with which to stir the mixture, and an error in the chemical formula. I am, etc., A. PERCY SMITH. Phoenix Mills, Dartford. (a) DETERMINATION OF CHLORINE IN WATER.-BY ALLEN HAZEN ... 232 (b) DYNAMICAL THEORY OF ALBUMINOID AMMONIA.—BY ROBERT B. WARDER (concluded)... REPORT OF RECENT RESEARCHES AND IMPROVEMENTS IN ANALYTICAL PROCESSES(a) DEXTRIN IN GENUINE HONEY.-BY C. AMTHOR AND J. STERN (b) TREATMENT OF URANIUM RESIDUES.-BY D. LAUBE ... 238 ... ... ... 239 ... (c) ESTIMATION OF TANNIC ACID IN OAK BARK, WITH PERMANGANATE.-BY F. GANTTER PROCEEDINGS OF THE SOCIETY OF PUBLIC ANALYSTS. A MEETING of the Society was held at Burlington House on Wednesday, the 13th ult., the President, Mr. Adams, in the chair. The minutes of the London meeting in June and the Liverpool meeting in August were read and confirmed. Mr. W. H. Collins, Analytical Chemist, of Bolton-le-Moors, was proposed as a member. Mr. ADAMS read a paper "On a New Form of Air-bath," a model of which he exhibited and explained. Mr. ALLEN read a paper "On Possible Future Extensions of the Duties of Public Analysts." A prolonged discussion ensued on this, and ultimately, on the proposal of Dr. Muter, seconded by Dr. Johnstone, it was resolved "that Mr. Allen's paper be printed and circulated with the agenda for the next meeting, and that the discussion be adjourned until that meeting." A paper by Dr. H. Leffmann and W. Beam, "On Some Applications of Centrifugal Action to Laboratory Work," was also read. The next meeting of the Society will be held on Wednesday, the 11th inst., at 8 o'clock, A NEW FORM OF AIR-BATH. (Read at Meeting, November, 1889.) BEARING in mind the universal and indispensable utility of the air-bath to the chemical analyst, one might expect to find much variety and perfection in the design and construction of such an important piece of apparatus. Strange to say, this is not so. I very much doubt if there is to be found any piece of chemical apparatus in the chemist's laboratory that has received less attention, or stands more in need of it. This fact was forced upon my attention by the great difficulty found in bringing certain hygroscopic substances to a constant weight, and I soon discovered that the attempt was hopeless with the ordinary instrument, the reasons for which were not far to seek. In the first place, in the ordinary bath it is impossible to maintain a uniform temperature throughout the whole of the drying chamber, for, even with the help of a thermostat, though it may be regulated with accuracy for some one special portion, other parts will in all probability be found to be several, indeed many, degrees hotter or colder according to the circumstance, so that to dry a substance, say at 100° C., the bath, though regulated to stand at this point for the spot where the thermometer is placed, is no assurance that the thing to be dried is exposed to the temperature desired, and if the object is of any considerable bulk, the probability is that one portion of it may extend into a region that is much below a hundred, and another into a place that is much above a hundred. Naturally the greatest heat is found near the floor, where the thermometer is never placed, and the least heat at the sides and in the corners, where radiation and stagnation mostly takes place; but more especially it is cold in the line of draughts that proceed from the chinks of the door and through the primitive contrivance that is usually provided for ventilation. In these parts the temperature may be very little above that of the external atmosphere. No wonder then that the complete drying of delicate hygroscopic organic substances is found to be so difficult, for before the colder part can be made to give up the last trace of moisture that clings so tenaciously to it, the hotter is over dried and stands the risk of being charred. In a case like this there is nothing to be got by turning and twisting the thing round so as to expose alternately its various parts to the greater heat. In imagination one can see what occurs; by a process of distillation and condensation the same kind of transference of moisture from the hotter to the colder parts takes place as is seen to occur, for instance, when the attempt is made to dry a damp flask under similar circumstances. But even this picture by no means exhibits the whole of the perplexing difficulties of tracing and controlling the air currents in an ordinary air-bath. They are so erratic, so fortuitous, so delusive, and subject to such uncontrollable shiftings, that, practically speaking, it is a question whether thorough drying in such a case is possible without destruction of the substance. At all events the chances in favour of it are so slender as not to be relied upon. Reflecting upon these difficulties, the theory of a perfect method for air-drying suggested two things as indispensable. 1. A constant current of pure dry air brought to the desired degree of temperature before admission into the drying chamber. |