276 



SCIENCE- GOSSIP. 



CONDUCTED BY B. FOULKES-WINKS, M.R.P.S. 



EXPOSURE TABLE FOR FEBRUARY. 



The figures in the following table are worked ont for plates of 

 about 100 Hurter & Driffield. For plates of lower speed number 

 give more exposure in proportion. Thus plates of 50 H. & D. 

 would require just double the exposure. In the same way, 

 plates of a higher speed number will require proportionately 

 less exposure. ■ 



Time, 10 A.M. to 2 P.M. 



Between 9 and 10 a.m. and 2 and 3 p.m. double the 

 required exposure. 



The small figures represent seconds, large figures minutes. 

 The exposures are calculated for sunshine. If the weather is 

 cloudy, increase the exposure by half as much again ; if gloomy, 

 double the exposure. 



Photographic Convention op the United 

 Kingdom. — We understand that the Convention 

 will be held this year at Oxford under the Presi- 

 dency of Sir William J. Herschel, Bart. The 

 meetings will take place during the second week in 

 July, at the Municipal Building. We hear that the 

 secretary and local committee are already making 

 extensive arrangements for visiting the most 

 interesting and picturesque places in the locality. 

 In Oxford alone the amateur might easily occupy 

 the time at his disposal ; but when we consider 

 that such places as Abingdon, Woodstock, Warwick, 

 etc., are within easy reach, we certainly think that 

 the committee are to be congratulated upon their 

 selection for this year's Convention. We expect to 

 see one of the largest gatherings on record, and, 

 judging from our experience at Oxford and its 

 vicinity, we are sure the amateur and professional 

 will spend a very enjoyable week, and return with 

 plenty of charming views. Readers wishing to 

 attend should write to Mr. F. A. Bridge, East 

 Lodge, Dalston Lane, London. N.E., who will give 

 every information. 



Snow Pictures. — Amateurs who put away their 

 camera in the late autumn, and do not bring it out 

 again until the spring, often miss some very charm- 

 ing effects when the snow is on the ground. We 

 believe there are a number of workers who do this 



every year, for we often hear the remark, " Oh, it 

 is no use bringing the camera out in the winter." 

 Quite recently we saw some exceedingly pretty 

 effects taken when the snow had just fallen, and 

 as we shall probably experience severe weather 

 during February, the amateur will be well advised 

 to have his camera ready for emergencies in this 

 direction. The best results are generally obtained 

 on slow plates with a full exposure. For develop- 

 ing these snow pictures we prefer a weak developer 

 of the metol type so as to ensure getting all possi- 

 ble detail. The selection of the process by which 

 the negative is to be printed is worthy of considera- 

 tion. The most natural and pleasing results are 

 obtained on platinotype paper. If this process is 

 to be used, it is advisable to make the negative 

 fairly strong, or, in other words, to let the nega- 

 tive show greater contrast between light and shade. 

 As platinotjqse printing, however, is very trouble- 

 some at this time of the year, we would suggest that 

 the bromide process may be used to advantage. In 

 this respect we would refer the reader to last 

 month's issue of Science-Gossip, where we describe 

 the working of a slow bromide paper which is 

 most suitable for this purpose. If, however, it is 

 decided to finish pictures of this class in gelatino- 

 chloride printing-out paper (P.O. P.), we are 

 strongly in favour of a matt paper toned with 

 platinum. The following formula, given by the 

 Eastman Kodak Company, we have found work 

 well and have very satisfactory results. Stock 

 Solution. — Potassium chloroplatinite, 5 grains ; 

 citric acid, 40 grains ; sodium chloride (common 

 salt), 40 grains ; water, 20 ounces. This bath will 

 keep well for a month. Wash the prints for about 

 five minutes in several changes of water and then 

 immerse in the above bath ; examine the prints by 

 transmitted light. Tone the prints to a deep 

 chocolate colour, rinse slightly, and then place in 

 the following bath to stop action of the toning bath 

 if a warm sepia tone is desired. Bath. — Sodium 

 carbonate (washing soda), J ounce ; water, 20 

 ounces. Rinse, and transfer to the fixing bath. 

 Fixing Bath. — Sodium hyposulphite, 3 ounces - T 

 water, 20 ounces. The prints" should be kept 

 moving about in the fixing bath for about ten 

 minutes. Wash thoroughly and dry between blot- 

 ting boards or by suspending them from print clips. 



A Toning Bath fob P.O.P. — Whilst on the 

 subject of printing on P.O.P. we should like to 

 draw attention to a new formula which has, in our 

 hands, given most pleasing tones, and is free from 

 the objectionable double-toning so often met with 

 in ordinary toning baths. We append the formula 

 which we consider to give the best results : — Stock 

 Solution — Amnion, sulphocyanide, 20 grains; com- 

 mon salt, 200 grains ; water, 20 ounces. To tone, 

 add one or two drams of the following solution : — 

 Chloride of gold, 15 grains ; water, 2 ounces. The 

 prints may be immersed in the solution without 

 any previous washing, and will tone in a few 

 minutes. Fix for about ten minutes in a bath as 

 follows: — Hyposulphite of soda, 3 ounces ; water, 

 20 ounces. Wash thoroughly and dry. 



Fading Negatives. — Writing to "Nature," on 

 January 17th, Mr. "William J. S. Lockyer draws 

 attention to the disappearance of 'images on 

 astronomical photographic plates, and gives in- 

 stances of faint objects after a time disappearing. 

 He mentions a process accomplished by Sir- William 

 Crookes for successfully bringing them back to 

 view, and gives Sir William's formula. 



