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A form of reflectometer for measuring the show through tendencies of printing papers is described. Its grading of a series of nineteen papers covering a wide range of opacity is in good agreement with the judgment of 173 trade observers. The instrument can also be used for measuring reflexion factors. Diffuse illumination, normal viewing and normal illumination, diffuse viewing can both be used and are shown experimentally to be practically equivalent, but the latter is more convenient. The opacity figures can be converted to the U.S. TAPPI Opacities by means of an equation due to Judd: the results obtained are in good agreement with measurements made on the American Bausch and Lomb Opacimeter.

The Barkas analysis is applied to a series of nine papers of known visual gloss. With some reservations, the analysis is found to hold approximately and the distribution of mirror facets so derived is found to accord well with the surface structure of the papers as found by microscopic examination. It is concluded that, whilst the analysis is of negligible value for practical gloss determinations, it appears to present a useful method of investigating the surface structure and "finish" of paper and similar delicate materials. The gloss of the papers examined appears to be assessed solely by the intensity of the light reflected at the specular angle and not by the contrast noted by examination at different angles nor by the ratio of specularly-reflected to diffusely-reflected light. Some suggestions for future research are given.

A goniophotometer for determining to an accuracy of about 1% the reflecting properties of surfaces of low and medium gloss is described. The instrument is particularly suitable for the measurement of papers and boards, and works off the ordinary electric light mains. Arrangement is made for the inclusion of Polaroid and coloured filters when desired. The specimen holder may be rotated about two axes, perpendicular to and parallel to, the plane of incidence, and the specimen itself may be rotated in its own plane through 360°. The photometer consists of a barrier layer type photocell connected to a Tinsley galvanometer. Two specimen polar curves obtained with the instrument are reproduced.

Investigations into the lone reproduction of offset lithographic processes are reviewed. The ideal contact screens for deep-etch plates are described and the effect of platemaking variables on dot size is discussed. The properties of the paper used for printing are shown to have an important influence on highlight and shadow contrast. Finally, it is shown that similar type screen negatives are required both for deep-etch plates and powderless etched letterpress blocks.

Measurements made on magnesium oxide deposited to a depth of 2 mm. on aluminium show that, for angles of incidence up to 60°, the polar reflexion curves are in general ellipses, and not the circles required by Lambert's law. For angles of incidence less than 45°, the major axis of the ellipse is perpendicular to the plane of the test surface, while for angles of incidence-from 45° to 60° the minor axis of the ellipse is perpendicular to this plane. At 45° incidence, the ellipse degenerates to a circle, and in this special case only, Lambert's law is obeyed to within the accuracy of the measurements. For angles of incidence greater than 60°, the curves become quite irregular, and at almost grazing incidence there is a distinct reddish specular component in the reflected light. An attempt is made to analyse the curves into specular and diffuse components by Barkas's method, but the results suggest that this method is not really applicable in the present instance. 45° appears to be a suitable angle of incidence to adopt in practical gloss determinations.

The performance of the Bausch and Lomb and Sheen glossmeters is examined. Comparison of gradings of nine printing papers according to visual and instrumental means shows that, despite high correlation between them, there are nevertheless important discrepancies not attributable to sampling, instrumental or personal errors. The effect of angle of incidence and viewing on grading is investigated; best results are noted at 45°, and the discrepancies become more pronounced at greater angles. Gradings of the same papers according to the Jones, Askania, Goerz, Ostwald and Klughardt methods are examined; all are found unsatisfactory. It is concluded that, for the limited range of papers tested, the most satisfactory grading is given by measurements of the intensity of light received when angles of incidence and viewing are 45°.

For a range of papers of luminance factor varying from 20% upwards and of gloss varying from almost complete matt to gloss high enough to give fair mirror images the equation G = S(a + 10/L) is proposed, where G is a measure of visual gloss, S is the relative intensity of reflected light under 45° - 45° conditions of illuminating and viewing, L is the luminance factor expressed as a percentage and a is a constant which, under the conditions used by the authors, is approximately 0.20. The visual gradings of eight papers out of ten are not markedly affected by the conditions of observation, but for the remaining two there is a highly significant shift in grading according to whether these conditions permit formation of mirror images or not. Gloss is considered to be a gestalt, corresponding to no single physical property of a surface, being judged by appraisal of a physical situation taken as a whole. The validity of the method used in establishing the psychological gloss scale is checked by experiments in weight grading.

Offset Lithography is to-day one of the most important printing processes. Although it has many advantages, it nevertheless suffers from two serious drawbacks, the first of which is the thinness of the ink film applied to paper. On account of this thinness, the optical density of the applied film rarely exceeds 14, corresponding to a reflection factor of about four per cent, and the maximum depth of tone is a dark grey rather than a good black.

THE word ‘rheology’ was coined in the United States in 1929 to denote the science of the deformation and flow of matter. Though the name is new, the science itself is old, and man has had a practical knowledge of some of the main facts of rheology since very early times. The phrase “rheological phenomena” may sound learned and forbidding; yet we study these “phenomena” every time we spread butter over bread with a knife, grease a motor-car, paint a garden shed or ‘help” children make sand castles. If it be of any advantage to man to improve bread, butter, cheese, jam, chocolate, inks, paints, varnishes, textiles, building materials and a host of other everyday commodities—without which civilization as we know it could not exist—then the study of rheology needs no further justification.

(1) LIKE everything else which has grown up as a result of an evolutionary process, the present musical notation1 has imperfections ; yet it remains superior to our ordinary orthography. It is universally accepted, and there is nothing in it corresponding to the English 'ough' sounds, or to, for example, the differences in the French and Italian pronunciations of 'un' and 'le'.

THE superheating and 'bumping' of some liquids is well known to organic chemists, but I wonder if the dangers of superheating are sufficiently widely realized. The following incident occurred recently.

MUCH of the technique of the paper mill laboratory is specialized and described only in papers distributed throughout an extensive literature: it is therefore useful to have in this single volume short descriptions of the most reliable methods of procedure, and references for those who wish to study any particular subject in detail. Probably because of an attempt to keep down the bulk of the volume, many of these descriptions are unfortunately rather sketchy and it is doubtful whether the mill chemist, approaching a given determination for the first time, could in all cases complete it successfully from the brief instructions given. For the same reason, the text is not very critical, nor does it discuss fully the difficulties which one is apt to encounter in practice; so that in general it conveys the impression that the determinations are easier to carry out than they really are. This book, then, should be regarded not as a substitute for a library, nor as a collection of instructions to be followed blindly on all occasions, but rather as a guide to methods and a pointer to sources of information. A Laboratory Handbook of Pulp and Paper Manufacture Incorporating the fourth edition of Stevens's Paper Mill Chemist. By Dr. Julius Grant. Pp. viii + 320 + 8 plates. (London: Edward Arnold and Co., 1942.) 28s. net.

WE have completed a psycho-physical study of the gloss of several series of coated and uncoated papers differing widely in surface finish and in colour, including a black, a green and a mauve, besides an assortment of shades of white, cream, yellow and brown.

Pressurized Packaging (Aerosols) By A. Herzka and J. Pickthall. Pp. xi + 411. (London: Butterworths Scientific Publications; New York: Academic Press, Inc., 1958.) 63s.