Name, etc.

Date,

Sig

Use to half gallon, of warm water as directed.

Signature.

(32) Write a prescription for a solution of potassium permanganate so that when a teaspoonful is added to a quart of water it will make a solution of about 1 to 5000.

Discussion,

A quart of water weighs nearly 15,000 grains, so 3 grains of the salt would be the amount necessary in each teaspoonful.

Name. etc.

Date,

M.

Sig

Use teaspoonful to quart of water as directed.

Signature.

(33) You wish to have a patient use douches of a gallon of 1 to 5000 potassium permanganate solution. Write the necessary prescription.

Discussion.

A pint of water weighs about 7500 grains, so 1 1/2 grains of the salt would be required for 1 pint. A gallon contains 8 pints, so would require about 12 grains. Tablets are inconvenient for patient's use and a solution should be ordered. It should be so concentrated that the smallest possible domestic measureful can be added to a gallon of water to give the required strength. Twelve grains will just comfortably dissolve in 1/2 fluidounce (1 tablespoonful) of water. If about a dozen douches are indicated the prescription should be for 6 fluidounces as follows:

Name, etc.

Date,

M.

Sig

Use tablespoonful to gallon of hot water as directed.

Signature.

(34) If you wish to prescribe a solution for a wet bichloride dressing for a poor patient, how will you write the prescription so that the patient can use 1 part to 10 parts of water and get a solution of about 1 to 5000?

Discussion.

An ounce of water weighs about 450 grains, so 1 grain of the salt would give a solution (by weight) of about 1 to 450. If 10 more ounces of water (about 4500 grains) are added to this, it gives a solution of about 1 to 5000.

Name, etc.

Date,

M.

Sig

Use 1 part to 10 parts of water to wet dressing.

Signature.

(35) Write a prescription for mercurial inunctions so that each dose will contain about 15 grains of metallic mercury.

Discussion.

The official ointment is too strong for continued use and the diluted is undesirable for systemic effect on account of the petrolatum content. The ointment contains 50 per cent. of metallic mercury, and if diluted half it will contain 25 per cent. If it is arranged to use 1 drachm of this ointment to each inunction it gives 15 grains of mercury.

Initials of patient.

Date,

M. ft. cht. cer. no. xvj.

Sig

Apply one each night as directed.

Signature.

(36) Write a prescription for chloroform liniment and soap liniment to make 6 fluidounces, so that the finished product will contain about 10 per c.ent. of chloroform.

Discussion.

Chloroform liniment contains 30 per cent. of chloroform and the solution wanted is one-third as strong (10 per cent.), so if one-third of the prescription is chloroform liniment, it will give the necessary reduction.

The percentage strength of the preparation (30) is to the percentage strength desired (10), as the number of ounces of prescription (6) is to the number of ounces of the preparation required (X).

30: 10:: 6: X=2.

Name of patient, etc. Date,

M.

Sig

Apply as directed.

Signature.

(37) A mother gave her baby five feedings of 6 fluidounces each. Her formula calls for 6 per cent. of lime water. How much calcium hydroxide does the child receive daily?

Discussion.

Five feedings of 6 fluidounces each totals 30 fluidounces; 6 per cent. of this is 1.8 fluidounces (lime water). Lime-water contains about 0.14 per cent. of calcium hydroxide-0.14 per cent. of 1.8 fluidounces (864 minims) = 0.0014x864 = 1.2 (grains calcium hydroxide).

(38) Write a prescription for a 4-fluidounce saturated solution of boric acid.

Discussion.

It is not practical to get a solution as concentrated as would be indicated by the stated solubility of the drug, as that only indicates the total amount soluble under the most favorable conditions and by the expenditure of unlimited time. If a prescriber merely orders a"Saturated Solution,"the druggist usually triturates an excess of the drug with water for a few moments and filters. It is better to prescribe a definite amount and know what the patient is receiving.

Boric acid is stated to be soluble in 18 parts water. That is 1 grain to dissolve in about 18 minims of water, but practically it is best not to order over 1 grain to 20 minims of water, or 24 grains to the fluidounce (480 minims).

Name of patient, etc.

Date,

M. ft. sol.

Sig

Apply locally as directed.

Signature.

(39) Write a metric prescription calling for 3 fluidounces of a saturated solution of potassium chlorate.

Discussion.

Potassium chlorate is said to be soluble in 11.5 parts of water or 1 grain in about 11.5 minims of water, but, making the usual allowance, as suggested in discussing the previous problem, it is better not to use more than 1 grain to 15 minims, or 32 grains to the fluidounce (480 minims), or 90 grains to the 3 fluidounces. Using the rule for transposing to metric equivalents (p. 336), the prescription would be as follows:

Name of patient, etc.

Date,

M. ft. sol.

Sig

Use for throat as directed.

(40) What may occur when a wet bichloride dressing is applied' to a surface previously painted with tincture of iodine?

Discussion.

The following reaction may result: HgCl2 plus 2 1 = Hgl2 plus 2 CI. Red mercuric iodide is a powerful irritant, and may cause extensive vesication, etc.