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معدات للغرفة المظلمة ..
الخريجين ..
موازين كيميائية ..
GRADUATES
A full assortment of graduates is an essential for every darkroom . The smaller graduates should be the accurate conical type with etched calibrations , but above sixteen ounces the cheaper , moulded - glass type will be good enough for most purposes if they are not used to measure less than half of their contents .
A good working assortment of graduates for the complete darkroom is as follows :
10 cc Etched calibration
1 ounce Etched calibration
2 ounces Etched calibration
8 ounces Etched calibration
32 ounces Molded or etched calibration
64 ounces Stainless steel or Steel enameled with internal calibration
Use the 64 - ounce graduate for diluting stock solutions or for measuring such solutions as hypo and stop - baths , where accuracy is relatively unimportant .
CHEMICAL BALANCES
It is now possible for photographers to buy ready - made formulas for all their standard processing solutions , and quite a few photographers , therefore , get along very nicely without the need of any sort of darkroom balance . However , should you prefer to mix your own formulas because of the saving in money and the greater flexibility this gives you , a photographic balance is essential . Unfor tunately , there are not many good balances for the photographic trade . If you prefer to buy most of your formulas ready mixed , you will find that a low - priced balance weighing up to two ounces will take care of your requirements well enough . There are several such balances on the market . A typical one has a sliding weight on a calibrated beam to weigh up to fifty grains , and separate weights up to two ounces .
If you like to compound all your own formulas and will , therefore , use your chemical balance more often , you will undoubtedly prefer a better and more accurate instrument . In that case , buy it from a laboratory supply firm . A good balance should come equipped with two or three sliding weights and weigh up to either 250 grams or eight ounces ( Figure 21 ) . Since most formulas are now given in both the avoirdupois and metric systems , a balance calibrated in either system
can be used with equal facil ity . The metric system is preferred , however , because it lends itself much more conveniently to calculation .
A minor inconvenience arising from the use of the metric system of weights and measures in the United States is that the glass bottles ordinarily available to the photographer for keeping his stock solutions do not come in metric sizes . This usually isn't too im portant because the metric unit of volume , the liter ( 1000 cc . ) , is only slightly larger than one quart ( 33.81 ounces or 1.05 liquid quarts ) . Many quart bottles are slightly oversize and will hold one liter if filled to the top . If not , you can call a quart a liter without any . trouble , since this will cause a difference in concentration of solutions of only 5 % per cent , which is seldom appreciable . In those rare cases where extreme accuracy is essential , you may refigure the formula by multiplying all gram figures by 0.95 , or else use 5 per cent less stock solution because of its greater concentration .
Figure 21 Weighing chemicals on a pair of filter papers is a good way to keep your balance clean and un contaminated .
In addition to a fine balance for small weights , you may want a scale reading in pounds for rough work , such as mixing hypo . However , it is easy enough to calibrate a metal can for measuring hypo by scratching or drawing a line to represent one or two pounds . Another simple system is to measure out hypo by volume , using an ordinary graduate .
The volume of a pound of hypo will vary somewhat with the size of the crystals , so weigh out one pound accurately and note its exact volume . This volume can then be used for hypo of the same crystal size in the future . As a rough guide , a pound of rice - crystal hypo has a volume of fifteen ounces when poured into the graduate without being shaken down to compact it . Larger crystals will come to about sixteen ounces in volume per pound . The strength of the hypo is not critical , and an error of as much as 10 per cent in measuring it will never be noticed .
Always keep the darkroom balance scrupulously clean so as not to contaminate your photographic chemicals . The best system is to cut up a number of squares of paper just big enough for the balance pan and use a fresh paper every time you mix a formula . You can weigh each sheet of paper beforehand and jot the weight down in pencil . If the balance has two pans , a simpler method is to use one paper on each pan , checking first to see that they balance perfectly .
If the slight extra cost is not particularly important , buy a package of round filter papers for your paper - weighing slips . Filter paper is uniform , so you need weigh only one sheet ; mark this weight on the package for a permanent record .
When weighing out chemicals , put a slight crease in your slip of paper by folding it lightly and straightening it out again . The crease will help when pouring the chemical into the water . Be sure to tap the paper sharply to get off any residue that may be clinging to it so as not to contaminate the next chemical . If you should accidentally weigh out too much , don't pour any of it back . Instead , use a small slip of clean paper to pick some off the top of the pile to be sure you aren't getting any of the chemicals previously weighed .
معدات للغرفة المظلمة ..
الخريجين ..
موازين كيميائية ..
GRADUATES
A full assortment of graduates is an essential for every darkroom . The smaller graduates should be the accurate conical type with etched calibrations , but above sixteen ounces the cheaper , moulded - glass type will be good enough for most purposes if they are not used to measure less than half of their contents .
A good working assortment of graduates for the complete darkroom is as follows :
10 cc Etched calibration
1 ounce Etched calibration
2 ounces Etched calibration
8 ounces Etched calibration
32 ounces Molded or etched calibration
64 ounces Stainless steel or Steel enameled with internal calibration
Use the 64 - ounce graduate for diluting stock solutions or for measuring such solutions as hypo and stop - baths , where accuracy is relatively unimportant .
CHEMICAL BALANCES
It is now possible for photographers to buy ready - made formulas for all their standard processing solutions , and quite a few photographers , therefore , get along very nicely without the need of any sort of darkroom balance . However , should you prefer to mix your own formulas because of the saving in money and the greater flexibility this gives you , a photographic balance is essential . Unfor tunately , there are not many good balances for the photographic trade . If you prefer to buy most of your formulas ready mixed , you will find that a low - priced balance weighing up to two ounces will take care of your requirements well enough . There are several such balances on the market . A typical one has a sliding weight on a calibrated beam to weigh up to fifty grains , and separate weights up to two ounces .
If you like to compound all your own formulas and will , therefore , use your chemical balance more often , you will undoubtedly prefer a better and more accurate instrument . In that case , buy it from a laboratory supply firm . A good balance should come equipped with two or three sliding weights and weigh up to either 250 grams or eight ounces ( Figure 21 ) . Since most formulas are now given in both the avoirdupois and metric systems , a balance calibrated in either system
can be used with equal facil ity . The metric system is preferred , however , because it lends itself much more conveniently to calculation .
A minor inconvenience arising from the use of the metric system of weights and measures in the United States is that the glass bottles ordinarily available to the photographer for keeping his stock solutions do not come in metric sizes . This usually isn't too im portant because the metric unit of volume , the liter ( 1000 cc . ) , is only slightly larger than one quart ( 33.81 ounces or 1.05 liquid quarts ) . Many quart bottles are slightly oversize and will hold one liter if filled to the top . If not , you can call a quart a liter without any . trouble , since this will cause a difference in concentration of solutions of only 5 % per cent , which is seldom appreciable . In those rare cases where extreme accuracy is essential , you may refigure the formula by multiplying all gram figures by 0.95 , or else use 5 per cent less stock solution because of its greater concentration .
Figure 21 Weighing chemicals on a pair of filter papers is a good way to keep your balance clean and un contaminated .
In addition to a fine balance for small weights , you may want a scale reading in pounds for rough work , such as mixing hypo . However , it is easy enough to calibrate a metal can for measuring hypo by scratching or drawing a line to represent one or two pounds . Another simple system is to measure out hypo by volume , using an ordinary graduate .
The volume of a pound of hypo will vary somewhat with the size of the crystals , so weigh out one pound accurately and note its exact volume . This volume can then be used for hypo of the same crystal size in the future . As a rough guide , a pound of rice - crystal hypo has a volume of fifteen ounces when poured into the graduate without being shaken down to compact it . Larger crystals will come to about sixteen ounces in volume per pound . The strength of the hypo is not critical , and an error of as much as 10 per cent in measuring it will never be noticed .
Always keep the darkroom balance scrupulously clean so as not to contaminate your photographic chemicals . The best system is to cut up a number of squares of paper just big enough for the balance pan and use a fresh paper every time you mix a formula . You can weigh each sheet of paper beforehand and jot the weight down in pencil . If the balance has two pans , a simpler method is to use one paper on each pan , checking first to see that they balance perfectly .
If the slight extra cost is not particularly important , buy a package of round filter papers for your paper - weighing slips . Filter paper is uniform , so you need weigh only one sheet ; mark this weight on the package for a permanent record .
When weighing out chemicals , put a slight crease in your slip of paper by folding it lightly and straightening it out again . The crease will help when pouring the chemical into the water . Be sure to tap the paper sharply to get off any residue that may be clinging to it so as not to contaminate the next chemical . If you should accidentally weigh out too much , don't pour any of it back . Instead , use a small slip of clean paper to pick some off the top of the pile to be sure you aren't getting any of the chemicals previously weighed .
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