Crookes. 1914.

Pure elementary silicon.

3854'00 3853.812 3856.20 3856.193 3862.75 3862-743

Remarks.

This is a well defined group of one sharp line followed by two broad nebulous bands. The first of these bands at

3856 193 is the strongest. I find no evidence on any of my photographs of the line given by Exner and Haschek at 3853 62. My line at 3853-812 is certainly not a double one. The line given by Exner and Haschek at 3883 46 is not shown on my photographs, and Lunt (Roy. Proc. Soc., lxxvi., 122) regards it as an impurity.

5961.6 5982'0

6342

6369'7*

6370

These two lines are faint and very nebulous. They were measured by means of the recording instrument described in this paper.

6346.962) These are a pair of strong lines in the red. They were measured 6371'032 from photographs taken on Panchromatic films, giving seven hours' exposure.

}

On examining my photographs under high magnifying power very faint lines can be seen in about these positions, but they are too faint to admit of trustworthy measurement.

taining spectrum lines in the desired gap. Some of the standard lines chosen have not been measured as accurately as those of iron; therefore my measurements based on such lines have not the same degree of accuracy as the lines measured against an iron standard. In some cases, however, I have been able to re-standardise the lines in the silicon used, by measuring them against iron lines near enough for this purpose, but not near enough to the

silicon lines.

There are two lines of silicon in the orange-red portion of the spectrum, extremely faint and hazy in appearance; to get their image with the most sensitive panchromatic films required an exposure of many hours with the 5-prism quartz train. I therefore used for these lines an instrument designed some years ago whereby eye observations could be taken and recorded with the 5-prism spectrograph.

The apparatus shown in outline drawing, Fig. 2, takes the place usually occupied by the camera in the 5-prism spectrograph. It consists essentially of a telescope, AB, furnished with the usual micrometer eyepiece, A, and fine wires. The object lens, B, is mounted on an accurately cut screw, c, of one-hundredth of an inch pitch; by rotating the screw the lens B is moved sideways so as to traverse the spectrum over the wires in the eyepiece A; the prolongation of the screw c carries a brass drum, D, 1 inch in diameter, which has ten needle points equally spaced round it. A narrow roll of paper, E, is mounted on a spool just above the drum D, and one end of the paper is pressed on its surface by a soft rubber roller, F. Rotating the drum D therefore draws the paper off the spool E, and imprints on it ten perforations for each revolution of the drum. As one revolution of drum carries the object glass one-hundredth of an inch sideways across the lines under measurement, and the drum is 1 inch in diameter, the space between each perforation equals 1/1000th of an inch movement of the object glass. (The actual distance apart of the dots on the paper is o'3146 of an inch). For convenience of calculation one of the needle points is doubled, so as to note each complete revolution. This device of marking the distances on the paper at the same moment as recording the lines eliminates any uncertainty that would otherwise be due to subsequent unequal alteration in the length of the paper.

The paper band, on its way from the spool E to the drum D, passes over a small table, F; at this point a fine pen, G, carried on a slide, can be made to trace a line any desired length across the strip of paper by pressure of the finger upon the lever H.

The method of measurement is as follows:- By rotating the screw, the spectrum is made to traverse the field of view, and when the line to be recorded coincides with the fine wires in the eyepiece, a touch of the finger on the lever, H, draws an ink record across the paper strip. When all the lines are recorded the paper strip is removed, and the distance between the dots on the paper can be subdivided into 10 parts by means of a transparent scale, by which the distance apart of any of the recorded lines can easily be measured. From these measurements the wave-lengths of the lines can be calculated in the same way as if the measurements were taken from a photograph. The distance apart of the sodium lines D, and D2, recorded on the paper strip, is 23 mm.

A good method of correcting these paper records is to take several observations upon each line in succession, moving the line backwards over the fine wire between each record. In the case of very sharp lines the records practically are in the same place. In other cases the ink lines may not be exactly superposed, because the lines to be measured are faint and hazy, and differences in position of the records are due to the almost insuperable difficulty of the eye hitting on the exact centre of the nebulosity.

The first published record of the silicon spectrum is by G. Salet in 1873, who gave the wave-lengths of nine lines in the visible part of the spectrum from the orange to violet (Ann. de Chim. et de Phys., xxvii., 65). His numbers differ from those of later observers, and as there are more accurate determinations of wave-lengths, I have omitted them as of no present value.

30

In 1893 and 1898 Rowland published the wave-length of lines occurring in the solar spectrum, ascribed by him to silicon ("A Preliminary Table of Solar Spectrum Wavelengths," Chicago; "A New Table of Standard Wavelengths," Phil. Trans., xxxvi., 49).

In 1900 Sir Norman Lockyer gave the wave-lengths o 14 lines in the blue part of the spectrum (Roy. Soc. Proc., Ixvii., 403). He used silicon bromide in a vacuum tube and elementary silicon.

In 1901 Sir Walter Noel Hartley gave the wave-lengths of eight lines photographically recorded in the ultra-violet part of the spectrum (Roy. Soc. Proc., lviii., 179; this paper is a revision, as far as the wave-lengths are concerned, of measurements of the lines published by the same observer in 1883). He obtained them by saturating one of the carbon poles with sodium silicate. In 1902 Exner and Haschek published a list of 45 wavelengths of lines in the silicon spectrum from the extreme ultra-violet to the blue ("Wellenlangen-Tabellen für Spektral-analytische Untersuchungen," Leipzig and Wien). sodium silicate on platinum wire, gave a list of silicon lines In 1903 A. de Gramont, using elementary silicon and partly selected for astronomical comparisons (CHEMICAL NEWS, Ixxxviii., 238; a paper read before the British Association, Southport Meeting).

In 1905 J. Lunt gave a list of nine lines of silicon, in the blue portion of the spectrum (Roy. Soc. Proc., Ixxvi., 118). These were seen in various vacuum tubes.

In the same year E. B. Frost and J. A. Brown, using elementary silicon and titanium prepared in the electric furnace, made careful measurements of three silicon lines selected as being of especial utility in determinations of the radial velocity of numerous stars (Astrophys. Journ., xxii., 157, 260).

In 1908 de Gramont, in conjunction with C. de Watteville, using silicon poles in an atmosphere of hydrogen, published a further list of 23 lines ranging from the extreme ultra-violet to the point in the violet where de Gramont's earlier list commenced (Comptes Rendus, cxlvii.,

239).

In 1911 Eder and Valenta published a list of 28 lines in the silicon spectrum, mostly in the ultra-violet portion and extending down to the blue ("Atlas Typischer Spectrum," Wien).

In the accompanying Tables I give the wave-lengths of the silicon lines measured by the observers named above. Earlier spectrum observations were necessarily imperfect, chiefly because of the difficulty in getting elementary silicon even in an approximate state of purity. Some observers also have limited the range of their observations to a small part of the spectrum, for astronomical and other

reasons.

Liberation of Nitrogen in the Reaction of NaOBr on Urea.-C. Alberto Garcia.-The author finds that with his nitrometer he always gets values very closely approximating to the theoretical values for the nitrogen in urea, even with solutions of different concentrations. This he attributes to the fact that he works in vacuo, and it appears that when the gas liberated by a reaction is determined in presence of substances in solution, the operation should always he performed in vacuo. Otherwise the liberation of gas is not complete, for some always remains dissolved in the solvent.-Bull. Soc. Chim, de France, xv.-xvi., No. 12.

Calculated for
C104H92016.
Per cent.

C=78.16
H = 5·81

O = 16'03

Found for Phenol + CH2O.

Per cent. Percent.

78'04 77'95

5'79

597

Found for

Saligenin + Phenol.

Per cent. Per cent.

78.16 78.24 5.65 5'75

16.17 16.08 16.19 16.01

That the end of the molecular chain in the individual, made as described above, cannot have a CH2OH group attached to the benzene ring is evident from the fact that the reaction between anhydrous phenol and hexamethylenetetramine could not produce such a substance, especially since, as will be shown presently, the only by. product from the reaction is ammonia. The other end of the molecule is hydroxylated, probably, as the substance is readily soluble in alkalis.

The H2O may be either a water of hydration which attached itself to the molecule during the process of solution and precipitation, or, which seems more reasonable, the process is one of oxidation, for the individual changes its colour from yellow to green when it dissolves in alkali and from green to red when it is precipitated by acid. The drying of the pptd. material at 50° C. changes the colour further to a reddish brown. This possible oxidation is described at further length (see prox.). Such a formula would have a molecular weight for C104H920161552 or for CooH800141384. The highest formula weight calculated from the rise in boiling-point which Dr. Baekeland has found for novolak dissolved in acetic acid is 1216 (Fourn. Indust. and Eng. Chem., 1909, i., 545).

Aylesworth (Brit. Pat. 4396, 1911) in his U.S. patent 1,029,737 lays claim to the production of a soluble phenolic resin formed from phenol and formaldehyde by boiling 2 mols. of phenol in I mol. of aqueous formaldehyde until a resin is produced having the formula C6H5.OCH2.C6H4.OCH2.C6H4OH (H. Lebach, Journ. Soc. Chem. Ind., 1913, xxxii., 561) as shown by boiling. point analysis. This is quite impossible for the reason that such a resin is not an individual but may be dissolved up in KOH and separated into two constituents by the addition of HCl, the precipitate containing approximately 50 per cent and the filtrate holding in solution approximately

• Journal of Industrial and Engineering Chemistry, vi., No. 1.

50 per cent of the original phenol used. The rise in the boiling-point given by Aylesworth is no doubt caused by the 50 per cent free phenol and shows that the molecule of the resin is so large in the precipitate as to have very little effect upon the boiling-point of the solvent employed, as the rise in the boiling-point may be accounted for by the free phenol present.

methylenes and 13 phenols is from the fact that the total A further proof that the molecule consisting of 12 is precipitated by the acid as described above, corresponds amount of resin formed in a phenol solution, and which in weight to 64 phenols to each 6 methylenes added or 13 phenols to 12 methylenes. This is in agreement with the combustion analysis, and with the highest number obtained in the rise of boiling-points. The formula then which we propose for this soluble resin is

C6H5OCH2(C6H4OCH2)11.C6H4OH, and following Kraut's suggested nomenclature we have called this material phenyl-endeka-saligeno-saligenin (Ann. der Chem., clvi., 123).

That this resin is an intermediate product which later is transformed by being mixed with formaldehyde or hexamethylenetetramine and heated into the insoluble infusible methylene phenol condensation products of the highest dielectric and tensile strength and chemical inertness, is almost certain from the fact that an aggregate can be made consisting of 10 mols. of phenol to 1 mol. of hexamethylenetetramine and this heated until all the ammonia has been evolved, which results in a heavy, viscous yellow transparent liquid when hot and semi-solid when cold, consisting of over 63 per cent phenyl-endekasaligeno-saligenin (novolak), the rest being water-soluble phenols; hexamethylenetetramine is then added in such proportions as to make the total phenol to methylene in the ratio of 1: I and heated until the mass has become a yellow porous sponge, the mass is then powdered and pressed in moulds at 200° C. and 12,000 lbs. per sq. in. for 5-10 mins. and the resin becomes a transparent amberlike material with a dielectric strength of 50-90,000 volts. per mm., an ohmic resistance of 2× 109 per cm3. and a tensile strength of 4000-4500 lbs. per sq. inch.

That a substance consisting of more than 60 per cent phenyl-endeka-saligeno-saligenin and the remainder a water-soluble phenol is transformed by the addition of hexamethylenetetramine and further heating into an insoluble substance of such high dielectric and tensile strength, seems to preclude the possibility of this resin remaining unchanged or transforming into any other product than an insoluble infusible resin of highest dielectric and tensile strength. For it must be remembered that this resin, of itself, is more brittle than cheap rosin and soluble in all the ordinary solvents.

Indeed we have found this intermediate substance present in all the materials we have made of whatever variety, soluble or insoluble, whether heated for a long or short period and whether at a high or relatively low temperature. Low temperature, a short time of heating, and excess phenol, or what is the same thing, not enough hexamethylenetetramine to make a 6 mols. of phenol to 1 mol. of hexamethylenetetramine resin gives a greater percentage of this soluble resin. It is also present in small proportions in 6: I resins that have been heated for many hours at 200° C.

Table I. gives the result of a few analyses of resins as described.

When the soluble, brittle, fusible resin is mixed, powdered, and heated for one hour with hexamethylenetetramine in the proportions of 6 mols. of novolak to I mol. of hexamethylenetetramine, assuming I mol. of novolak, CooH800141384, the mass becomes largely insoluble in all ordinary solvents, caustic alkalis, &c. It swells or gelatinises in boiling phenol but does not dissolve and exhibits generally the properties of the insoluble products. The final resin formed from the novolak and hexamethylenetetramine is much darker than the