Another Formula.
For large plates, 20 lbs. perchloride of iron and distilled water, until weight amounts to 1.500 grammes per 1000 c.c. From this four (4) solutions are made, at
| No. 1, 42 | deg. | Beaumé; | spec. grav. | 1.420 |
| No. 2, 38 | " | " | " | 1.375 |
| No. 3, 35 | " | " | " | 1.330 |
| No. 4, 31 | " | " | " | 1.285 |
The plate is now ready for biting. Keep a record of the bitings, and length of time for each one, for after-study; also note the time of exposure of the tissue, age of same, etc., etc.
Pour the acid from a glass graduate with one sweep over the plate, removing all bubbles with a feather, noting the time of immersion so as to guide you. Start with 42 deg., having ready the 37 deg. in another graduate, watch carefully the action of the acid, and if the resist has been properly printed, the action of the acid will show after a minute; if longer it means a generally longer biting for each bath.