1. .1 I Compounds of the general formul [wherein one of R^ and represents a hydrogen atom and the other of R^ and represents a lower alkyl group or R^ represents a hydrogen atom and R2 represents 1 an alkanoyl group containing 1 to 5 carbon atoms or R-L and R? together represent an orthocarboxyl group 1 of a lower alkenoyl containing 1· to 5 carbon. toms or a group of formula \ / C I 40328/2 (wherein A and B, which may be the same or different, each represents a hydrogen atom or an alkyl group with the proviso that A and B do not both represent hydrogen atoms; or A and B together with the carbon atom to which they are attached represent a 5- or 6-membered alicyclic ring)] . 2. pompounds according to olaim 1 with the exception', of those wherein R.^ and R? together represent an orthocarboxyl group of B lower alkanoyl containing 1 to 5 carbon atoms. 3. 22-Fluoro-3' ' '-acetyl-digoxin. 4. 22-Pluoro-3' ' ' ,4' ' '-isopropylidene-digoxin. 5. Compounds as claimed in claim 2, with the exception of those 'compounds claimed in claim 3» and claim 4, as herein specifically disclosed. 6. Compounds according to Claim 1, wherein R.. and R 2 together represent an orthocarboxyl group of a lower alkanoyl containing 1 to 5 carbon atoms. 7. A process for thf preparation of compounds as claimed in claim 2 which comprises acylating, alkylating, acetali ing ) 40328/2 ,8. A process as claimed in claim "3! wherein the acylation is effected by reaction of the compound of formula II with an orthocarboxylate, followed by partial acid hydrolysis of the 3' '' ,4' ' '-orthocarboxylate first obtained. A process as claimed in claim 8 wherein the 3·'', 4 ' ' '-orthocarboxylate intermediate is obtained by trans- esterification of the compound of formula II with an excess of an appropriate aliphatic trialkyl orthocarboxylate. l'O, A process as claimed in claim 8 or claim 9 wherein the compound of formula II is reacted with the orthocarboxylate in the presence of an acid catalyst. 11. A process as claimed in claim ID wherein the said acid catalyst is fluoroboric acid, hydrochloric acid, sulfuric acid, p_-toluenesulfonic acid, trichloroacetic acid, boron trifluoride etherate or an acidic ion exchanger. 12!. A process as claimed in any of claims 8 to I'lwherein the reaction of the compound of formula II with the orthocarboxylate is effected in the presence of an inert solvent. \ 40328/2 13 . A process as claimed in claim 12 wherein the solvent is dimethylglycol, tetrahydrofuran or '■; N-methylpyrrolidone . i 14' . A process as claimed in any of claims 8 to 13 wherein the said partial hydrolysis is effected using an aqueous acid at a pH of 4 or less. l5i A process as claimed in claim 7 wherein the alkylation is effected by means of a diazoalkane. lfi. A process as claimed in claim 15 wherein the diazoalkane is diazomethane , 17 . A process as claimed in claim 1$ or claim 16 wherein the reaction is effected in the presence of a dilute acid. 1© .. A process as claimed in claim 17> wherein the dilute acid is fluoroboric acid, aluminium isopropylate, iron(lll) chloride, boric acid or a trialkyl borate.' 19 . A process as claimed in claim 7 wherein the alkylation is effected by means of an alkyl halide or dialkyl sulfate. 20 . A process as claimed in claim 19 wherein the reaction is effected in the presence of an acid binding agent. ., 21. A process as claimed in claim 20' wherein the acid binding agent is a mixture of barium hydroxide and barium oxide . 22. A process as claimed in any of claims 13 to 20 wherein the reaction is effected in the presence of an inert solvent. 23. A process as claimed in claim 23 wherein the solvent is methylene chloride, dimethylformamide or a mixture thereof. 24. A process as claimed in claim 7> wherein the ketalisation is effected by reacting the compound of formula II with an aliphatic ketone, 25. A process as claimed in claim 24 wherein the reaction' is effected in the presence of a dehydrating agent. 26. A process as claimed in claim 2§ wherein the dehydrating agent is anhydrous copper sulfate, hydrogen chloride, p-toluenesulfonic acid, boron trifluoride etherate, zinc chloride or an acid ion exchanger. 27;. A process as claimed in any of claims 2 to 26 wherein the reaction is effected at a temperature of from 20 'to 30°C. 28. A process as claimed in claim 7 wherein the ketal-isation is effected by reacting the compound of formula II with a dialkylketal. 29. i A process as claimed in claim 28 wherein the dialkylketal is a dimethylketal . 30. A process as claimed in claim 28 or claim} 29 wherein the reaction is effected in the presence of a. catalytic quantity of an acid. 31. A process as claimed in claim?30 wherein the acid is hydrogen chloride or p_-toluenesulfonic acid, 3 ' A prpcess as claimed in any of claims, 28 to' 31 wherein the reaction is effected in the presence of a trace of water. 33. A process for the preparation of compounds as claimed in claim 2 wherein R~ represents an alkanoyl group ^ carbon atoms ■ ■' ■ 5t - and R^ represents a hydrogen atom which comprises subjecting to partial hydrolysis a compound of formula I wherein R^ and together represent an orthocarboxylate group. 34. , A process as claimed in claim 33 wherein the said partial hydrolysis is effected using an aqueous acid at a pH of 4 or less. 35·1 A process for the preparation of compounds as claimed in claim 2 substantially as herein described. 3β· A process for the preparation of compounds a© claimed in claim 2 substantially as herein described in any of Examples 1 to 8. 37. Compounds according to claim 2 when prepared b a process as claimed in any of claims 7 to 36. 38. A process for the preparation of compounds as claimed in claim 6 which comprises reacting a compound of formula II herein with an orthocarboxylate. 39· A process as claimed in claim 38 wherein the reaction io effected byacansesterlflcatlon of the compound of ormula II with an excess of an aliphatic trialkyl orthocarboxylate. 40· A process as claimed in claim 38 or claim 39 wherein the reaction is effected in the presence of an acid catalyst. 41. process as claimed in claim 40 whereinHie said acid catalyst is fluoroboric acid, hydrochloric acid, sulfuric add, p-tolueneaulfonlc acid, trichloroacetic acid, boron trifluoride etherate or an acidic ion exchanger. 42. A process as claimed In any of claims 38 to 41 wherein the ssactlo is effected in the presence of an inert solvent. 43. A process as claimed in claim 42 wherein the solvent is dimetbylglycol, tdrahydrofuran or U-methyl-pyrrolid ae, 44· process for the preparation of compounds as claimed In claim 6 substantially as herein described i any of Example Q 1 to 3· 45. Compaiunds as claimed in claim 6 when prepared by a process as claimed in any of claims 38 to 44. V 40328/2 46· Pharmaceutical compositions comprising as active ingredient a compound as claimed in claim 2 in association with a pharmaceutical carrier or excipient. 47. Compositions as claimed in claim 46 in a form suitable for oral, rectal or parenteral administration. 48. Compositions as claimed in claim 46 or claim 4? in the form of dosage units. 49· Compositions as claimed in claim 48 wherein each os¾o unit contains from 0.125 to 2.00 mg of a compound as claimed in claim 2. 50. Pharmaceutical compositions substantially as herein described in any of Examples I to VII.